From fd67593a8bfbf890d8dfbdcc1167495a1d05f58b Mon Sep 17 00:00:00 2001
From: HarrisL2 <harris.yh.lau@gmail.com>
Date: Tue, 2 Dec 2025 19:41:42 -0500
Subject: [PATCH] Mark relevant types as Nullable

---
 build.sbt                                     | 10 +++++
 jvm/src/test/scala/scala/xml/XMLTest.scala    | 25 +++++++------
 .../scala/xml/ScalaVersionSpecific.scala      | 10 +++--
 .../main/scala-2/scala/xml/Nullables.scala    | 21 +++++++++++
 .../main/scala-3/scala/xml/Nullables.scala    | 16 ++++++++
 .../src/main/scala/scala/xml/Attribute.scala  | 27 +++++++-------
 .../src/main/scala/scala/xml/Document.scala   |  9 +++--
 shared/src/main/scala/scala/xml/Elem.scala    | 13 ++++---
 .../src/main/scala/scala/xml/MetaData.scala   | 37 ++++++++++---------
 .../scala/scala/xml/NamespaceBinding.scala    | 21 ++++++-----
 shared/src/main/scala/scala/xml/Node.scala    | 13 ++++---
 shared/src/main/scala/scala/xml/Null.scala    | 17 +++++----
 .../scala/scala/xml/PrefixedAttribute.scala   | 17 +++++----
 shared/src/main/scala/scala/xml/QNode.scala   |  3 +-
 .../src/main/scala/scala/xml/TopScope.scala   |  5 ++-
 .../scala/scala/xml/UnprefixedAttribute.scala | 19 +++++-----
 shared/src/main/scala/scala/xml/Utility.scala | 29 ++++++++-------
 shared/src/main/scala/scala/xml/XML.scala     |  5 ++-
 shared/src/main/scala/scala/xml/dtd/DTD.scala |  3 +-
 .../src/main/scala/scala/xml/dtd/Decl.scala   |  5 ++-
 .../main/scala/scala/xml/dtd/ExternalID.scala | 15 ++++----
 .../include/CircularIncludeException.scala    |  4 +-
 .../UnavailableResourceException.scala        |  4 +-
 .../scala/xml/include/XIncludeException.scala |  8 ++--
 .../xml/include/sax/EncodingHeuristics.scala  |  9 +++--
 .../xml/include/sax/XIncludeFilter.scala      |  7 ++--
 .../scala/xml/include/sax/XIncluder.scala     |  5 ++-
 .../xml/parsing/ConstructingHandler.scala     |  4 +-
 .../xml/parsing/DefaultMarkupHandler.scala    |  4 +-
 .../scala/xml/parsing/FactoryAdapter.scala    | 21 ++++++-----
 .../scala/xml/parsing/MarkupHandler.scala     | 11 +++---
 .../scala/xml/parsing/MarkupParser.scala      | 35 +++++++++---------
 .../xml/parsing/NoBindingFactoryAdapter.scala |  3 +-
 .../test/scala/scala/xml/AttributeTest.scala  |  3 +-
 .../test/scala/scala/xml/MetaDataTest.scala   |  7 ++--
 .../test/scala/scala/xml/NodeSeqTest.scala    |  1 +
 shared/src/test/scala/scala/xml/XMLTest.scala | 19 +++++-----
 37 files changed, 276 insertions(+), 189 deletions(-)
 create mode 100644 shared/src/main/scala-2/scala/xml/Nullables.scala
 create mode 100644 shared/src/main/scala-3/scala/xml/Nullables.scala

diff --git a/build.sbt b/build.sbt
index d1fd9a4f8..c061bf752 100644
--- a/build.sbt
+++ b/build.sbt
@@ -110,6 +110,16 @@ lazy val xml = crossProject(JSPlatform, JVMPlatform, NativePlatform)
         ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.Null.get"),
         ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.Node.attribute"),
 
+        // Nullable types result in a raw Seq, is fixed in 3.8
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.Attribute.unapply"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.Attribute.apply"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.Attribute.value"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.MetaData.value"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.PrefixedAttribute.unapply"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.PrefixedAttribute.this"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.UnprefixedAttribute.unapply"),
+        ProblemFilters.exclude[IncompatibleSignatureProblem]("scala.xml.UnprefixedAttribute.this"),
+
         // trait Attribute now extends trait ScalaVersionSpecificMetaData to ensure the previous signatures
         // with return type `collection.Seq` remain valid.
         // (trait Attribute extends MetaData, but that parent is not present in bytecode because it's a class.)
diff --git a/jvm/src/test/scala/scala/xml/XMLTest.scala b/jvm/src/test/scala/scala/xml/XMLTest.scala
index 4e5dba1a6..41b0df5b6 100644
--- a/jvm/src/test/scala/scala/xml/XMLTest.scala
+++ b/jvm/src/test/scala/scala/xml/XMLTest.scala
@@ -8,6 +8,7 @@ import java.net.URL
 import scala.xml.dtd.{DocType, PublicID}
 import scala.xml.parsing.ConstructingParser
 import scala.xml.Utility.sort
+import xml.Nullables._
 
 object XMLTestJVM {
   val e: MetaData = Null //Node.NoAttributes
@@ -17,7 +18,7 @@ object XMLTestJVM {
 class XMLTestJVM {
   import XMLTestJVM.{e, sc}
 
-  def Elem(prefix: String, label: String, attributes: MetaData, scope: NamespaceBinding, child: Node*): Elem =
+  def Elem(prefix: Nullable[String], label: String, attributes: MetaData, scope: NamespaceBinding, child: Node*): Elem =
     scala.xml.Elem.apply(prefix, label, attributes, scope, minimizeEmpty = true, child: _*)
 
   lazy val parsedxml1: Elem = XML.loadString("<hello><world/></hello>")
@@ -385,9 +386,9 @@ class XMLTestJVM {
 
   @UnitTest
   def t5052(): Unit = {
-    assertTrue(<elem attr={ null: String }/> xml_== <elem/>)
+    assertTrue(<elem attr={ null: Nullable[String] }/> xml_== <elem/>)
     assertTrue(<elem attr={ None }/> xml_== <elem/>)
-    assertTrue(<elem/> xml_== <elem attr={ null: String }/>)
+    assertTrue(<elem/> xml_== <elem attr={ null: Nullable[String] }/>)
     assertTrue(<elem/> xml_== <elem attr={ None }/>)
   }
 
@@ -400,9 +401,9 @@ class XMLTestJVM {
     assertHonorsIterableContract(<a y={ None }/>.attributes)
     assertHonorsIterableContract(<a y={ None } x=""/>.attributes)
     assertHonorsIterableContract(<a a="" y={ None }/>.attributes)
-    assertHonorsIterableContract(<a y={ null: String }/>.attributes)
-    assertHonorsIterableContract(<a y={ null: String } x=""/>.attributes)
-    assertHonorsIterableContract(<a a="" y={ null: String }/>.attributes)
+    assertHonorsIterableContract(<a y={ null: Nullable[String] }/>.attributes)
+    assertHonorsIterableContract(<a y={ null: Nullable[String] } x=""/>.attributes)
+    assertHonorsIterableContract(<a a="" y={ null: Nullable[String] }/>.attributes)
   }
 
   @UnitTest
@@ -459,9 +460,9 @@ class XMLTestJVM {
   @UnitTest
   def attributes(): Unit = {
     val noAttr: Elem = <t/>
-    val attrNull: Elem = <t a={ null: String }/>
+    val attrNull: Elem = <t a={ null: Nullable[String] }/>
     val attrNone: Elem = <t a={ None: Option[Seq[Node]] }/>
-    val preAttrNull: Elem = <t p:a={ null: String }/>
+    val preAttrNull: Elem = <t p:a={ null: Nullable[String] }/>
     val preAttrNone: Elem = <t p:a={ None: Option[Seq[Node]] }/>
     assertEquals(noAttr, attrNull)
     assertEquals(noAttr, attrNone)
@@ -469,8 +470,8 @@ class XMLTestJVM {
     assertEquals(noAttr, preAttrNone)
 
     val xml1: Elem = <t b="1" d="2"/>
-    val xml2: Elem = <t a={ null: String } p:a={ null: String } b="1" c={ null: String } d="2"/>
-    val xml3: Elem = <t b="1" c={ null: String } d="2" a={ null: String } p:a={ null: String }/>
+    val xml2: Elem = <t a={ null: Nullable[String] } p:a={ null: Nullable[String] } b="1" c={ null: Nullable[String] } d="2"/>
+    val xml3: Elem = <t b="1" c={ null: Nullable[String] } d="2" a={ null: Nullable[String] } p:a={ null: Nullable[String] }/>
     assertEquals(xml1, xml2)
     assertEquals(xml1, xml3)
 
@@ -759,8 +760,8 @@ class XMLTestJVM {
   def documentBaseURI(): Unit = {
     val url: URL = resourceUrl("site")
     // XMLLoader returns the document's baseURI:
-    assert(XML.withSAXParser(xercesInternal.newSAXParser).loadDocument(url).baseURI.endsWith("/test-classes/scala/xml/site.xml"))
-    assert(XML.withSAXParser(xercesExternal.newSAXParser).loadDocument(url).baseURI.endsWith("/test-classes/scala/xml/site.xml"))
+    assert(XML.withSAXParser(xercesInternal.newSAXParser).loadDocument(url).baseURI.nn.endsWith("/test-classes/scala/xml/site.xml"))
+    assert(XML.withSAXParser(xercesExternal.newSAXParser).loadDocument(url).baseURI.nn.endsWith("/test-classes/scala/xml/site.xml"))
     // ConstructingParser does not return it of course: since it uses scala.io.Source it has no idea where is the XML coming from:
     assertNull(ConstructingParser.fromSource(scala.io.Source.fromURI(url.toURI), preserveWS = false).document().baseURI)
   }
diff --git a/shared/src/main/scala-2.13+/scala/xml/ScalaVersionSpecific.scala b/shared/src/main/scala-2.13+/scala/xml/ScalaVersionSpecific.scala
index 49da95b8b..979ffb407 100644
--- a/shared/src/main/scala-2.13+/scala/xml/ScalaVersionSpecific.scala
+++ b/shared/src/main/scala-2.13+/scala/xml/ScalaVersionSpecific.scala
@@ -12,6 +12,8 @@
 
 package scala.xml
 
+
+import xml.Nullables._
 import scala.collection.immutable.StrictOptimizedSeqOps
 import scala.collection.{View, SeqOps, IterableOnce, immutable, mutable}
 import scala.collection.BuildFrom
@@ -65,11 +67,11 @@ private[xml] trait ScalaVersionSpecificNode { self: Node =>
 }
 
 private[xml] trait ScalaVersionSpecificMetaData { self: MetaData =>
-  def apply(key: String): scala.collection.Seq[Node]
-  def apply(namespace_uri: String, owner: Node, key: String): scala.collection.Seq[Node]
-  def apply(namespace_uri: String, scp: NamespaceBinding, k: String): scala.collection.Seq[Node]
+  def apply(key: String): Nullable[scala.collection.Seq[Node]]
+  def apply(namespace_uri: String, owner: Node, key: Nullable[String]): Nullable[scala.collection.Seq[Node]]
+  def apply(namespace_uri: Nullable[String], scp: NamespaceBinding, k: Nullable[String]): Nullable[scala.collection.Seq[Node]]
 
-  def value: scala.collection.Seq[Node]
+  def value: Nullable[scala.collection.Seq[Node]]
 }
 
 private[xml] trait ScalaVersionSpecificTextBuffer { self: TextBuffer =>
diff --git a/shared/src/main/scala-2/scala/xml/Nullables.scala b/shared/src/main/scala-2/scala/xml/Nullables.scala
new file mode 100644
index 000000000..707939c91
--- /dev/null
+++ b/shared/src/main/scala-2/scala/xml/Nullables.scala
@@ -0,0 +1,21 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc.
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.xml
+object Nullables {
+    type Nullable[T] = T
+    implicit class NonNullOps[T](private val x: T) extends AnyVal {
+        def nn: T = {
+            x
+        }
+    }
+}
diff --git a/shared/src/main/scala-3/scala/xml/Nullables.scala b/shared/src/main/scala-3/scala/xml/Nullables.scala
new file mode 100644
index 000000000..41417080c
--- /dev/null
+++ b/shared/src/main/scala-3/scala/xml/Nullables.scala
@@ -0,0 +1,16 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc.
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.xml
+object Nullables {
+  type Nullable[T] = T | Null
+}
diff --git a/shared/src/main/scala/scala/xml/Attribute.scala b/shared/src/main/scala/scala/xml/Attribute.scala
index 1c7c35750..50078d076 100644
--- a/shared/src/main/scala/scala/xml/Attribute.scala
+++ b/shared/src/main/scala/scala/xml/Attribute.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 import scala.collection.Seq
 
 /**
@@ -22,21 +23,21 @@ import scala.collection.Seq
  *  @author  Burak Emir
  */
 object Attribute {
-  def unapply(x: Attribute): Option[(String, Seq[Node], MetaData)] = x match {
+  def unapply(x: Attribute): Option[(Nullable[String], Nullable[Seq[Node]], MetaData)] = x match {
     case PrefixedAttribute(_, key, value, next) => Some((key, value, next))
     case UnprefixedAttribute(key, value, next)  => Some((key, value, next))
     case _                                      => None
   }
 
   /** Convenience functions which choose Un/Prefixedness appropriately */
-  def apply(key: String, value: Seq[Node], next: MetaData): Attribute =
+  def apply(key: Nullable[String], value: Seq[Node], next: MetaData): Attribute =
     new UnprefixedAttribute(key, value, next)
 
-  def apply(pre: String, key: String, value: String, next: MetaData): Attribute =
+  def apply(pre: Nullable[String], key: String, value: String, next: MetaData): Attribute =
     if (pre == null || pre == "") new UnprefixedAttribute(key, value, next)
     else new PrefixedAttribute(pre, key, value, next)
 
-  def apply(pre: String, key: String, value: Seq[Node], next: MetaData): Attribute =
+  def apply(pre: Nullable[String], key: String, value: Seq[Node], next: MetaData): Attribute =
     if (pre == null || pre == "") new UnprefixedAttribute(key, value, next)
     else new PrefixedAttribute(pre, key, value, next)
 
@@ -54,29 +55,29 @@ object Attribute {
  *  @author  Burak Emir
  */
 trait Attribute extends MetaData with ScalaVersionSpecificMetaData {
-  def pre: String // will be null if unprefixed
-  override val key: String
-  override val value: ScalaVersionSpecific.SeqOfNode
+  def pre: Nullable[String] // will be null if unprefixed
+  override val key: Nullable[String]
+  override val value: Nullable[ScalaVersionSpecific.SeqOfNode]
   override val next: MetaData
 
-  override def apply(key: String): ScalaVersionSpecific.SeqOfNode
-  override def apply(namespace: String, scope: NamespaceBinding, key: String): ScalaVersionSpecific.SeqOfNode
+  override def apply(key: String): Nullable[ScalaVersionSpecific.SeqOfNode]
+  override def apply(namespace: Nullable[String], scope: NamespaceBinding, key: Nullable[String]): Nullable[ScalaVersionSpecific.SeqOfNode]
   override def copy(next: MetaData): Attribute
 
-  override def remove(key: String): MetaData =
+  override def remove(key: Nullable[String]): MetaData =
     if (!isPrefixed && this.key == key) next
     else copy(next.remove(key))
 
-  override def remove(namespace: String, scope: NamespaceBinding, key: String): MetaData =
+  override def remove(namespace: Nullable[String], scope: NamespaceBinding, key: String): MetaData =
     if (this.key == key && scope.getURI(pre) == namespace) next
     else copy(next.remove(namespace, scope, key))
 
   override def isPrefixed: Boolean = pre != null
 
-  override def getNamespace(owner: Node): String
+  override def getNamespace(owner: Node): Nullable[String]
 
   override def wellformed(scope: NamespaceBinding): Boolean = {
-    val arg: String = if (isPrefixed) scope.getURI(pre) else null
+    val arg: Nullable[String] = if (isPrefixed) scope.getURI(pre) else null
     (next(arg, scope, key) == null) && next.wellformed(scope)
   }
 
diff --git a/shared/src/main/scala/scala/xml/Document.scala b/shared/src/main/scala/scala/xml/Document.scala
index 8fe1c6ae4..650018aa2 100644
--- a/shared/src/main/scala/scala/xml/Document.scala
+++ b/shared/src/main/scala/scala/xml/Document.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 
 import scala.collection.Seq
+import xml.Nullables._
 
 /**
  * A document information item (according to InfoSet spec). The comments
@@ -42,7 +43,7 @@ class Document extends NodeSeq with Serializable {
   var docElem: Node = _
 
   /** The dtd that comes with the document, if any */
-  var dtd: scala.xml.dtd.DTD = _
+  var dtd: Nullable[scala.xml.dtd.DTD] = _
 
   /**
    * An unordered set of notation information items, one for each notation
@@ -50,17 +51,17 @@ class Document extends NodeSeq with Serializable {
    *  has no value.
    */
   def notations: Seq[scala.xml.dtd.NotationDecl] =
-    dtd.notations
+    dtd.nn.notations
 
   /**
    * An unordered set of unparsed entity information items, one for each
    *  unparsed entity declared in the DTD.
    */
   def unparsedEntities: Seq[scala.xml.dtd.EntityDecl] =
-    dtd.unparsedEntities
+    dtd.nn.unparsedEntities
 
   /** The base URI of the document entity. */
-  var baseURI: String = _
+  var baseURI: Nullable[String] = _
 
   /**
    * The name of the character encoding scheme in which the document entity
diff --git a/shared/src/main/scala/scala/xml/Elem.scala b/shared/src/main/scala/scala/xml/Elem.scala
index 6b77f1642..426052fee 100755
--- a/shared/src/main/scala/scala/xml/Elem.scala
+++ b/shared/src/main/scala/scala/xml/Elem.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 
 import scala.collection.Seq
+import xml.Nullables._
 
 /**
  * This singleton object contains the `apply` and `unapplySeq` methods for
@@ -24,10 +25,10 @@ import scala.collection.Seq
 // Note: used by the Scala compiler.
 object Elem {
 
-  def apply(prefix: String, label: String, attributes: MetaData, scope: NamespaceBinding, minimizeEmpty: Boolean, child: Node*): Elem =
+  def apply(prefix: Nullable[String], label: Nullable[String], attributes: MetaData, scope: NamespaceBinding, minimizeEmpty: Boolean, child: Node*): Elem =
     new Elem(prefix, label, attributes, scope, minimizeEmpty, child: _*)
 
-  def unapplySeq(n: Node): Option[(String, String, MetaData, NamespaceBinding, ScalaVersionSpecific.SeqOfNode)] =
+  def unapplySeq(n: Node): Option[(Nullable[String], Nullable[String], MetaData, NamespaceBinding, ScalaVersionSpecific.SeqOfNode)] =
     n match {
       case _: SpecialNode | _: Group => None
       case _                         => Some((n.prefix, n.label, n.attributes, n.scope, n.child))
@@ -55,8 +56,8 @@ object Elem {
  */
 // Note: used by the Scala compiler.
 class Elem(
-  override val prefix: String,
-  override val label: String,
+  override val prefix: Nullable[String],
+  override val label: Nullable[String],
   attributes1: MetaData,
   override val scope: NamespaceBinding,
   val minimizeEmpty: Boolean,
@@ -98,8 +99,8 @@ class Elem(
    *  @return a new symbol with updated attributes
    */
   def copy(
-    prefix: String = this.prefix,
-    label: String = this.label,
+    prefix: Nullable[String] = this.prefix,
+    label: Nullable[String] = this.label,
     attributes: MetaData = this.attributes,
     scope: NamespaceBinding = this.scope,
     minimizeEmpty: Boolean = this.minimizeEmpty,
diff --git a/shared/src/main/scala/scala/xml/MetaData.scala b/shared/src/main/scala/scala/xml/MetaData.scala
index 6bdd080f0..b9842478a 100644
--- a/shared/src/main/scala/scala/xml/MetaData.scala
+++ b/shared/src/main/scala/scala/xml/MetaData.scala
@@ -17,6 +17,7 @@ import Utility.sbToString
 import scala.annotation.tailrec
 import scala.collection.AbstractIterable
 import scala.collection.Seq
+import xml.Nullables._
 
 object MetaData {
   /**
@@ -37,13 +38,13 @@ object MetaData {
    *  namespace URIs via the given scope.
    */
   def normalize(attribs: MetaData, scope: NamespaceBinding): MetaData = {
-    def iterate(md: MetaData, normalized_attribs: MetaData, set: Set[String]): MetaData =
+    def iterate(md: MetaData, normalized_attribs: MetaData, set: Set[Nullable[String]]): MetaData =
       if (md.isNull) {
         normalized_attribs
       } else if (md.value == null)
         iterate(md.next, normalized_attribs, set)
       else {
-        val key: String = getUniversalKey(md, scope)
+        val key: Nullable[String] = getUniversalKey(md, scope)
         if (set(key))
           iterate(md.next, normalized_attribs, set)
         else
@@ -56,8 +57,8 @@ object MetaData {
   /**
    * returns key if md is unprefixed, pre+key is md is prefixed
    */
-  def getUniversalKey(attrib: MetaData, scope: NamespaceBinding): String = attrib match {
-    case prefixed: PrefixedAttribute     => scope.getURI(prefixed.pre) + prefixed.key
+  def getUniversalKey(attrib: MetaData, scope: NamespaceBinding): Nullable[String] = attrib match {
+    case prefixed: PrefixedAttribute     => scope.getURI(prefixed.pre).asInstanceOf[String] + prefixed.key
     case unprefixed: UnprefixedAttribute => unprefixed.key
   }
 
@@ -107,7 +108,7 @@ abstract class MetaData
    * @param  key
    * @return value as Seq[Node] if key is found, null otherwise
    */
-  def apply(key: String): ScalaVersionSpecific.SeqOfNode
+  def apply(key: String): Nullable[ScalaVersionSpecific.SeqOfNode]
 
   /**
    * convenience method, same as `apply(namespace, owner.scope, key)`.
@@ -116,7 +117,7 @@ abstract class MetaData
    *  @param owner the element owning this attribute list
    *  @param key   the attribute key
    */
-  final def apply(namespace_uri: String, owner: Node, key: String): ScalaVersionSpecific.SeqOfNode =
+  final def apply(namespace_uri: String, owner: Node, key: Nullable[String]): Nullable[ScalaVersionSpecific.SeqOfNode] =
     apply(namespace_uri, owner.scope, key)
 
   /**
@@ -127,7 +128,7 @@ abstract class MetaData
    * @param  k   to be looked for
    * @return value as Seq[Node] if key is found, null otherwise
    */
-  def apply(namespace_uri: String, scp: NamespaceBinding, k: String): ScalaVersionSpecific.SeqOfNode
+  def apply(namespace_uri: Nullable[String], scp: NamespaceBinding, k: Nullable[String]): Nullable[ScalaVersionSpecific.SeqOfNode]
 
   /**
    * returns a copy of this MetaData item with next field set to argument.
@@ -135,7 +136,7 @@ abstract class MetaData
   def copy(next: MetaData): MetaData
 
   /** if owner is the element of this metadata item, returns namespace */
-  def getNamespace(owner: Node): String
+  def getNamespace(owner: Node): Nullable[String]
 
   def hasNext: Boolean = Null != next
 
@@ -166,16 +167,16 @@ abstract class MetaData
     }
 
   /** returns key of this MetaData item */
-  def key: String
+  def key: Nullable[String]
 
   /** returns value of this MetaData item */
-  def value: ScalaVersionSpecific.SeqOfNode
+  def value: Nullable[ScalaVersionSpecific.SeqOfNode]
 
   /**
    * Returns a String containing "prefix:key" if the first key is
    *  prefixed, and "key" otherwise.
    */
-  def prefixedKey: String = this match {
+  def prefixedKey: Nullable[String] = this match {
     case x: Attribute if x.isPrefixed => s"${x.pre}:$key"
     case _                            => key
   }
@@ -183,8 +184,8 @@ abstract class MetaData
   /**
    * Returns a Map containing the attributes stored as key/value pairs.
    */
-  def asAttrMap: Map[String, String] =
-    iterator.map(x => (x.prefixedKey, NodeSeq.fromSeq(x.value).text)).toMap
+  def asAttrMap: Map[Nullable[String], String] =
+    iterator.map(x => (x.prefixedKey, NodeSeq.fromSeq(x.value.nn).text)).toMap
 
   /** returns Null or the next MetaData item */
   def next: MetaData
@@ -195,7 +196,7 @@ abstract class MetaData
    * @param  key
    * @return value in Some(Seq[Node]) if key is found, None otherwise
    */
-  final def get(key: String): Option[ScalaVersionSpecific.SeqOfNode] = Option(apply(key))
+  final def get(key: String): Option[ScalaVersionSpecific.SeqOfNode] = Option(apply(key).asInstanceOf[ScalaVersionSpecific.SeqOfNode])
 
   /** same as get(uri, owner.scope, key) */
   final def get(uri: String, owner: Node, key: String): Option[ScalaVersionSpecific.SeqOfNode] =
@@ -209,8 +210,8 @@ abstract class MetaData
    * @param  key to be looked fore
    * @return value as `Some[Seq[Node]]` if key is found, None otherwise
    */
-  final def get(uri: String, scope: NamespaceBinding, key: String): Option[ScalaVersionSpecific.SeqOfNode] =
-    Option(apply(uri, scope, key))
+  final def get(uri: Nullable[String], scope: NamespaceBinding, key: String): Option[ScalaVersionSpecific.SeqOfNode] =
+    Option(apply(uri, scope, key).asInstanceOf[ScalaVersionSpecific.SeqOfNode])
 
   protected def toString1: String = sbToString(toString1)
 
@@ -229,9 +230,9 @@ abstract class MetaData
    */
   def wellformed(scope: NamespaceBinding): Boolean
 
-  def remove(key: String): MetaData
+  def remove(key: Nullable[String]): MetaData
 
-  def remove(namespace: String, scope: NamespaceBinding, key: String): MetaData
+  def remove(namespace: Nullable[String], scope: NamespaceBinding, key: String): MetaData
 
   final def remove(namespace: String, owner: Node, key: String): MetaData =
     remove(namespace, owner.scope, key)
diff --git a/shared/src/main/scala/scala/xml/NamespaceBinding.scala b/shared/src/main/scala/scala/xml/NamespaceBinding.scala
index 8efe27d79..c495931a0 100644
--- a/shared/src/main/scala/scala/xml/NamespaceBinding.scala
+++ b/shared/src/main/scala/scala/xml/NamespaceBinding.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 
 import scala.collection.Seq
+import xml.Nullables._
 
 /**
  * The class `NamespaceBinding` represents namespace bindings
@@ -25,12 +26,12 @@ import scala.collection.Seq
  */
 // Note: used by the Scala compiler.
 @SerialVersionUID(0 - 2518644165573446725L)
-case class NamespaceBinding(prefix: String, uri: String, parent: NamespaceBinding) extends AnyRef with Equality {
+case class NamespaceBinding(prefix: Nullable[String], uri: Nullable[String], parent: Nullable[NamespaceBinding]) extends AnyRef with Equality {
   if (prefix == "")
     throw new IllegalArgumentException("zero length prefix not allowed")
 
-  def getURI(prefix: String): String =
-    if (this.prefix == prefix) uri else parent.getURI(prefix)
+  def getURI(prefix: Nullable[String]): Nullable[String] =
+    if (this.prefix == prefix) uri else parent.nn.getURI(prefix)
 
   /**
    * Returns some prefix that is mapped to the URI.
@@ -39,21 +40,21 @@ case class NamespaceBinding(prefix: String, uri: String, parent: NamespaceBindin
    * @return the prefix that is mapped to the input URI, or null
    * if no prefix is mapped to the URI.
    */
-  def getPrefix(uri: String): String =
-    if (uri == this.uri) prefix else parent.getPrefix(uri)
+  def getPrefix(uri: String): Nullable[String] =
+    if (uri == this.uri) prefix else parent.nn.getPrefix(uri)
 
   override def toString: String = Utility.sbToString(buildString(_, TopScope))
 
   private def shadowRedefined(stop: NamespaceBinding): NamespaceBinding = {
-    def prefixList(x: NamespaceBinding): List[String] =
+    def prefixList(x: Nullable[NamespaceBinding]): List[Nullable[String]] =
       if ((x == null) || x.eq(stop)) Nil
       else x.prefix :: prefixList(x.parent)
-    def fromPrefixList(l: List[String]): NamespaceBinding = l match {
+    def fromPrefixList(l: List[Nullable[String]]): NamespaceBinding = l match {
       case Nil     => stop
       case x :: xs => NamespaceBinding(x, this.getURI(x), fromPrefixList(xs))
     }
-    val ps0: List[String] = prefixList(this).reverse
-    val ps: List[String] = ps0.distinct
+    val ps0: List[Nullable[String]] = prefixList(this).reverse
+    val ps: List[Nullable[String]] = ps0.distinct
     if (ps.size == ps0.size) this
     else fromPrefixList(ps)
   }
@@ -80,6 +81,6 @@ case class NamespaceBinding(prefix: String, uri: String, parent: NamespaceBindin
 
     val prefixStr: String = if (prefix != null) s":$prefix" else ""
     val uriStr: String = if (uri != null) uri else ""
-    parent.doBuildString(sb.append(s""" xmlns$prefixStr="$uriStr""""), stop) // copy(ignore)
+    parent.nn.doBuildString(sb.append(s""" xmlns$prefixStr="$uriStr""""), stop) // copy(ignore)
   }
 }
diff --git a/shared/src/main/scala/scala/xml/Node.scala b/shared/src/main/scala/scala/xml/Node.scala
index d9c41dd1e..c2a769524 100755
--- a/shared/src/main/scala/scala/xml/Node.scala
+++ b/shared/src/main/scala/scala/xml/Node.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 import scala.collection.Seq
 
 /**
@@ -28,7 +29,7 @@ object Node {
   /** the empty namespace */
   val EmptyNamespace: String = ""
 
-  def unapplySeq(n: Node): Some[(String, MetaData, ScalaVersionSpecific.SeqOfNode)] =
+  def unapplySeq(n: Node): Some[(Nullable[String], MetaData, ScalaVersionSpecific.SeqOfNode)] =
     Some((n.label, n.attributes, n.child))
 }
 
@@ -48,10 +49,10 @@ object Node {
 abstract class Node extends NodeSeq with ScalaVersionSpecificNode {
 
   /** prefix of this node */
-  def prefix: String = null
+  def prefix: Nullable[String] = null
 
   /** label of this node. I.e. "foo" for &lt;foo/&gt;) */
-  def label: String
+  def label: Nullable[String]
 
   /**
    * used internally. Atom/Molecule = -1 PI = -2 Comment = -3 EntityRef = -5
@@ -72,7 +73,7 @@ abstract class Node extends NodeSeq with ScalaVersionSpecificNode {
   /**
    *  convenience, same as `getNamespace(this.prefix)`
    */
-  def namespace: String = getNamespace(this.prefix)
+  def namespace: Nullable[String]  = getNamespace(this.prefix)
 
   /**
    * Convenience method, same as `scope.getURI(pre)` but additionally
@@ -82,7 +83,7 @@ abstract class Node extends NodeSeq with ScalaVersionSpecificNode {
    * @return    the namespace if `scope != null` and prefix was
    *            found, else `null`
    */
-  def getNamespace(pre: String): String = if (scope == null) null else scope.getURI(pre)
+  def getNamespace(pre: Nullable[String]): Nullable[String] = if (scope == null) null else scope.getURI(pre)
 
   /**
    * Convenience method, looks up an unprefixed attribute in attributes of this node.
@@ -190,7 +191,7 @@ abstract class Node extends NodeSeq with ScalaVersionSpecificNode {
   /**
    * Returns a type symbol (e.g. DTD, XSD), default `'''null'''`.
    */
-  def xmlType: TypeSymbol = null
+  def xmlType: Nullable[TypeSymbol] = null
 
   /**
    * Returns a text representation of this node. Note that this is not equivalent to
diff --git a/shared/src/main/scala/scala/xml/Null.scala b/shared/src/main/scala/scala/xml/Null.scala
index c8e35640c..6200e7f29 100644
--- a/shared/src/main/scala/scala/xml/Null.scala
+++ b/shared/src/main/scala/scala/xml/Null.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 import scala.collection.Iterator
 import scala.collection.Seq
 
@@ -31,12 +32,12 @@ case object Null extends MetaData {
   override def filter(f: MetaData => Boolean): ScalaVersionSpecificReturnTypes.NullFilter = this
 
   override def copy(next: MetaData): MetaData = next
-  override def getNamespace(owner: Node): ScalaVersionSpecificReturnTypes.NullGetNamespace = null
+  override def getNamespace(owner: Node): ScalaVersionSpecificReturnTypes.NullGetNamespace = null.asInstanceOf[ScalaVersionSpecificReturnTypes.NullGetNamespace]
 
   override def hasNext: Boolean = false
-  override def next: ScalaVersionSpecificReturnTypes.NullNext = null
-  override def key: ScalaVersionSpecificReturnTypes.NullKey = null
-  override def value: ScalaVersionSpecificReturnTypes.NullValue = null
+  override def next: ScalaVersionSpecificReturnTypes.NullNext = null.asInstanceOf[ScalaVersionSpecificReturnTypes.NullNext]
+  override def key: ScalaVersionSpecificReturnTypes.NullKey = null.asInstanceOf[ScalaVersionSpecificReturnTypes.NullKey]
+  override def value: ScalaVersionSpecificReturnTypes.NullValue = null.asInstanceOf[ScalaVersionSpecificReturnTypes.NullValue]
   override def isPrefixed: Boolean = false
 
   override def length: Int = 0
@@ -48,8 +49,8 @@ case object Null extends MetaData {
   }
   override protected def basisForHashCode: Seq[Any] = Nil
 
-  override def apply(namespace: String, scope: NamespaceBinding, key: String): ScalaVersionSpecificReturnTypes.NullApply3 = null
-  override def apply(key: String): ScalaVersionSpecific.SeqOfNode =
+  override def apply(namespace: Nullable[String], scope: NamespaceBinding, key: Nullable[String]): ScalaVersionSpecificReturnTypes.NullApply3 = null.asInstanceOf[ScalaVersionSpecificReturnTypes.NullApply3]
+  override def apply(key: String): Nullable[ScalaVersionSpecific.SeqOfNode] =
     if (Utility.isNameStart(key.head)) null
     else throw new IllegalArgumentException(s"not a valid attribute name '$key', so can never match !")
 
@@ -62,6 +63,6 @@ case object Null extends MetaData {
 
   override def wellformed(scope: NamespaceBinding): Boolean = true
 
-  override def remove(key: String): ScalaVersionSpecificReturnTypes.NullRemove = this
-  override def remove(namespace: String, scope: NamespaceBinding, key: String): ScalaVersionSpecificReturnTypes.NullRemove = this
+  override def remove(key: Nullable[String]): ScalaVersionSpecificReturnTypes.NullRemove = this
+  override def remove(namespace: Nullable[String], scope: NamespaceBinding, key: String): ScalaVersionSpecificReturnTypes.NullRemove = this
 }
diff --git a/shared/src/main/scala/scala/xml/PrefixedAttribute.scala b/shared/src/main/scala/scala/xml/PrefixedAttribute.scala
index 1dc6ba124..c6109cf33 100644
--- a/shared/src/main/scala/scala/xml/PrefixedAttribute.scala
+++ b/shared/src/main/scala/scala/xml/PrefixedAttribute.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 import scala.collection.Seq
 
 /**
@@ -27,12 +28,12 @@ import scala.collection.Seq
 class PrefixedAttribute(
   override val pre: String,
   override val key: String,
-  _value: Seq[Node],
+  _value: Nullable[Seq[Node]],
   val next1: MetaData
 )
   extends Attribute
 {
-  override val value: ScalaVersionSpecific.SeqOfNode = if (_value == null) null else _value match {
+  override val value: Nullable[ScalaVersionSpecific.SeqOfNode] = if (_value == null) null else _value match {
     case ns: ScalaVersionSpecific.SeqOfNode => ns
     case _ => _value.toVector
   }
@@ -40,8 +41,8 @@ class PrefixedAttribute(
   override val next: MetaData = if (value != null) next1 else next1.remove(key)
 
   /** same as this(pre, key, Text(value), next), or no attribute if value is null */
-  def this(pre: String, key: String, value: String, next: MetaData) =
-    this(pre, key, if (value != null) Text(value) else null: NodeSeq, next)
+  def this(pre: String, key: String, value: Nullable[String], next: MetaData) =
+    this(pre, key, if (value != null) Text(value) else null: Nullable[NodeSeq], next)
 
   /** same as this(pre, key, value.get, next), or no attribute if value is None */
   def this(pre: String, key: String, value: Option[Seq[Node]], next: MetaData) =
@@ -54,16 +55,16 @@ class PrefixedAttribute(
   override def copy(next: MetaData): PrefixedAttribute =
     new PrefixedAttribute(pre, key, value, next)
 
-  override def getNamespace(owner: Node): String =
+  override def getNamespace(owner: Node): Nullable[String] =
     owner.getNamespace(pre)
 
   /** forwards the call to next (because caller looks for unprefixed attribute */
-  override def apply(key: String): ScalaVersionSpecific.SeqOfNode = next(key)
+  override def apply(key: String): Nullable[ScalaVersionSpecific.SeqOfNode] = next(key)
 
   /**
    * gets attribute value of qualified (prefixed) attribute with given key
    */
-  override def apply(namespace: String, scope: NamespaceBinding, key: String): ScalaVersionSpecific.SeqOfNode =
+  override def apply(namespace: Nullable[String], scope: NamespaceBinding, key: Nullable[String]): Nullable[ScalaVersionSpecific.SeqOfNode] =
     if (key == this.key && scope.getURI(pre) == namespace)
       value
     else
@@ -71,5 +72,5 @@ class PrefixedAttribute(
 }
 
 object PrefixedAttribute {
-  def unapply(x: PrefixedAttribute): Some[(String, String, Seq[Node], MetaData)] = Some((x.pre, x.key, x.value, x.next))
+  def unapply(x: PrefixedAttribute): Some[(String, String, Nullable[Seq[Node]], MetaData)] = Some((x.pre, x.key, x.value, x.next))
 }
diff --git a/shared/src/main/scala/scala/xml/QNode.scala b/shared/src/main/scala/scala/xml/QNode.scala
index ddf7818c4..9d96eeecb 100644
--- a/shared/src/main/scala/scala/xml/QNode.scala
+++ b/shared/src/main/scala/scala/xml/QNode.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 /**
  * This object provides an extractor method to match a qualified node with
  *  its namespace URI
@@ -20,6 +21,6 @@ package xml
  *  @author  Burak Emir
  */
 object QNode {
-  def unapplySeq(n: Node): Some[(String, String, MetaData, ScalaVersionSpecific.SeqOfNode)] =
+  def unapplySeq(n: Node): Some[(Nullable[String], Nullable[String], MetaData, ScalaVersionSpecific.SeqOfNode)] =
     Some((n.scope.getURI(n.prefix), n.label, n.attributes, n.child))
 }
diff --git a/shared/src/main/scala/scala/xml/TopScope.scala b/shared/src/main/scala/scala/xml/TopScope.scala
index 0b82e4b63..a9c030256 100644
--- a/shared/src/main/scala/scala/xml/TopScope.scala
+++ b/shared/src/main/scala/scala/xml/TopScope.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 /**
  * top level namespace scope. only contains the predefined binding
  *  for the &quot;xml&quot; prefix which is bound to
@@ -20,10 +21,10 @@ package xml
  */
 object TopScope extends NamespaceBinding(null, null, null) {
 
-  override def getURI(prefix1: String): String =
+  override def getURI(prefix1: Nullable[String]): Nullable[String] =
     if (prefix1 == XML.xml) XML.namespace else null
 
-  override def getPrefix(uri1: String): String =
+  override def getPrefix(uri1: String): Nullable[String] =
     if (uri1 == XML.namespace) XML.xml else null
 
   override def toString: String = ""
diff --git a/shared/src/main/scala/scala/xml/UnprefixedAttribute.scala b/shared/src/main/scala/scala/xml/UnprefixedAttribute.scala
index 877a59b25..cdde2a9dc 100644
--- a/shared/src/main/scala/scala/xml/UnprefixedAttribute.scala
+++ b/shared/src/main/scala/scala/xml/UnprefixedAttribute.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 
+import xml.Nullables._
 import scala.collection.Seq
 
 /**
@@ -22,13 +23,13 @@ import scala.collection.Seq
  */
 // Note: used by the Scala compiler.
 class UnprefixedAttribute(
-  override val key: String,
-  _value: Seq[Node],
+  override val key: Nullable[String],
+  _value: Nullable[Seq[Node]],
   next1: MetaData
 )
   extends Attribute
 {
-  override val value: ScalaVersionSpecific.SeqOfNode = if (_value == null) null else _value match {
+  override val value: Nullable[ScalaVersionSpecific.SeqOfNode] = if (_value == null) null else _value match {
     case ns: ScalaVersionSpecific.SeqOfNode => ns
     case _ => _value.toVector
   }
@@ -37,8 +38,8 @@ class UnprefixedAttribute(
   override val next: MetaData = if (value != null) next1 else next1.remove(key)
 
   /** same as this(key, Text(value), next), or no attribute if value is null */
-  def this(key: String, value: String, next: MetaData) =
-    this(key, if (value != null) Text(value) else null: NodeSeq, next)
+  def this(key: String, value: Nullable[String], next: MetaData) =
+    this(key, if (value != null) Text(value) else null: Nullable[NodeSeq], next)
 
   /** same as this(key, value.get, next), or no attribute if value is None */
   def this(key: String, value: Option[Seq[Node]], next: MetaData) =
@@ -47,7 +48,7 @@ class UnprefixedAttribute(
   /** returns a copy of this unprefixed attribute with the given next field*/
   override def copy(next: MetaData): UnprefixedAttribute = new UnprefixedAttribute(key, value, next)
 
-  final override def getNamespace(owner: Node): String = null
+  final override def getNamespace(owner: Node): Nullable[String] = null
 
   /**
    * Gets value of unqualified (unprefixed) attribute with given key, null if not found
@@ -55,7 +56,7 @@ class UnprefixedAttribute(
    * @param  key
    * @return value as Seq[Node] if key is found, null otherwise
    */
-  override def apply(key: String): ScalaVersionSpecific.SeqOfNode =
+  override def apply(key: String): Nullable[ScalaVersionSpecific.SeqOfNode] =
     if (key == this.key) value else next(key)
 
   /**
@@ -66,9 +67,9 @@ class UnprefixedAttribute(
    * @param  key
    * @return ..
    */
-  override def apply(namespace: String, scope: NamespaceBinding, key: String): ScalaVersionSpecific.SeqOfNode =
+  override def apply(namespace: Nullable[String], scope: NamespaceBinding, key: Nullable[String]): Nullable[ScalaVersionSpecific.SeqOfNode] =
     next(namespace, scope, key)
 }
 object UnprefixedAttribute {
-  def unapply(x: UnprefixedAttribute): Some[(String, Seq[Node], MetaData)] = Some((x.key, x.value, x.next))
+  def unapply(x: UnprefixedAttribute): Some[(Nullable[String], Nullable[Seq[Node]], MetaData)] = Some((x.key, x.value, x.next))
 }
diff --git a/shared/src/main/scala/scala/xml/Utility.scala b/shared/src/main/scala/scala/xml/Utility.scala
index cf85be14f..68ed32cbe 100755
--- a/shared/src/main/scala/scala/xml/Utility.scala
+++ b/shared/src/main/scala/scala/xml/Utility.scala
@@ -18,6 +18,7 @@ import scala.collection.mutable
 import scala.language.implicitConversions
 import scala.collection.Seq
 import scala.collection.immutable.{Seq => ISeq}
+import xml.Nullables._
 
 /**
  * The `Utility` object provides utility functions for processing instances
@@ -78,9 +79,9 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
 
   /** returns a sorted attribute list */
   def sort(md: MetaData): MetaData = if (md.isNull || md.next.isNull) md else {
-    val key: String = md.key
-    val smaller: MetaData = sort(md.filter { m => m.key < key })
-    val greater: MetaData = sort(md.filter { m => m.key > key })
+    val key: String = md.key.nn
+    val smaller: MetaData = sort(md.filter { m => m.key.nn < key })
+    val greater: MetaData = sort(md.filter { m => m.key.nn > key })
     smaller.foldRight(md.copy(greater)) ((x, xs) => x.copy(xs))
   }
 
@@ -137,20 +138,20 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
    *
    * @return    `'''null'''` if `ref` was not a predefined entity.
    */
-  final def unescape(ref: String, s: StringBuilder): StringBuilder =
+  final def unescape(ref: String, s: StringBuilder): Nullable[StringBuilder] =
     unescMap.get(ref).map(s.append).orNull
 
   /**
    * Returns a set of all namespaces used in a sequence of nodes
    * and all their descendants, including the empty namespaces.
    */
-  def collectNamespaces(nodes: Seq[Node]): mutable.Set[String] =
-    nodes.foldLeft(new mutable.HashSet[String]) { (set, x) => collectNamespaces(x, set); set }
+  def collectNamespaces(nodes: Seq[Node]): mutable.Set[Nullable[String]] =
+    nodes.foldLeft(new mutable.HashSet[Nullable[String]]) { (set, x) => collectNamespaces(x, set); set }
 
   /**
    * Adds all namespaces in node to set.
    */
-  def collectNamespaces(n: Node, set: mutable.Set[String]): Unit =
+  def collectNamespaces(n: Node, set: mutable.Set[Nullable[String]]): Unit =
     if (n.doCollectNamespaces) {
       set += n.namespace
       for (a <- n.attributes) a match {
@@ -222,12 +223,12 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
     minimizeTags: MinimizeMode.Value,
     sb: StringBuilder
   ): Unit = {
-    @tailrec def ser(nss: List[List[Node]], pscopes: List[NamespaceBinding], spaced: List[Boolean], toClose: List[Node]): Unit = nss match {
+    @tailrec def ser(nss: List[List[Node]], pscopes: List[NamespaceBinding], spaced: List[Boolean], toClose: List[Nullable[Node]]): Unit = nss match {
       case List(Nil) =>
       case Nil :: rests =>
         if (toClose.head != null) {
           sb.append("</")
-          toClose.head.nameToString(sb)
+          toClose.head.nn.nameToString(sb)
           sb.append('>')
         }
         ser(rests, pscopes.tail, spaced.tail, toClose.tail)
@@ -296,7 +297,7 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
   /**
    * Returns a hashcode for the given constituents of a node
    */
-  def hashCode(pre: String, label: String, attribHashCode: Int, scpeHash: Int, children: Seq[Node]): Int =
+  def hashCode(pre: Nullable[String], label: Nullable[String], attribHashCode: Int, scpeHash: Int, children: Seq[Node]): Int =
     scala.util.hashing.MurmurHash3.orderedHash(label +: attribHashCode +: scpeHash +: children, pre.##)
 
   def appendQuoted(s: String): String = sbToString(appendQuoted(s, _))
@@ -323,7 +324,7 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
     sb.append('"')
   }
 
-  def getName(s: String, index: Int): String =
+  def getName(s: String, index: Int): Nullable[String] =
     if (index >= s.length) null else {
       val xs: String = s.drop(index)
       if (xs.nonEmpty && isNameStart(xs.head)) xs.takeWhile(isNameChar)
@@ -334,14 +335,14 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
    * Returns `'''null'''` if the value is a correct attribute value,
    * error message if it isn't.
    */
-  def checkAttributeValue(value: String): String = {
+  def checkAttributeValue(value: String): Nullable[String] = {
     var i: Int = 0
     while (i < value.length) {
       value.charAt(i) match {
         case '<' =>
           return "< not allowed in attribute value"
         case '&' =>
-          val n: String = getName(value, i + 1)
+          val n: Nullable[String] = getName(value, i + 1)
           if (n == null)
             return s"malformed entity reference in attribute value [$value]"
           i = i + n.length + 1
@@ -357,7 +358,7 @@ object Utility extends AnyRef with parsing.TokenTests with ScalaVersionSpecificU
   // unused, untested
   def parseAttributeValue(value: String): ScalaVersionSpecific.SeqOfNode = {
     val sb: StringBuilder = new StringBuilder
-    var rfb: StringBuilder = null
+    var rfb: Nullable[StringBuilder] = null
     val nb: NodeBuffer = new NodeBuffer()
 
     val it: Iterator[Char] = value.iterator
diff --git a/shared/src/main/scala/scala/xml/XML.scala b/shared/src/main/scala/scala/xml/XML.scala
index 3dfe36b27..dff151454 100755
--- a/shared/src/main/scala/scala/xml/XML.scala
+++ b/shared/src/main/scala/scala/xml/XML.scala
@@ -17,6 +17,7 @@ import factory.XMLLoader
 import java.io.{File, FileDescriptor, FileInputStream, FileOutputStream, InputStream, Reader, StringReader, Writer}
 import java.nio.channels.Channels
 import scala.util.control.Exception
+import xml.Nullables._
 
 object Source {
   def fromFile(name: String): InputSource = fromFile(new File(name))
@@ -96,7 +97,7 @@ object XML extends XMLLoader[Elem] {
     node: Node,
     enc: String = "UTF-8",
     xmlDecl: Boolean = false,
-    doctype: dtd.DocType = null
+    doctype: Nullable[dtd.DocType] = null
   ): Unit = {
     val fos: FileOutputStream = new FileOutputStream(filename)
     val w: Writer = Channels.newWriter(fos.getChannel, enc)
@@ -121,7 +122,7 @@ object XML extends XMLLoader[Elem] {
     node: Node,
     enc: String,
     xmlDecl: Boolean,
-    doctype: dtd.DocType,
+    doctype: Nullable[dtd.DocType],
     minimizeTags: MinimizeMode.Value = MinimizeMode.Default
   ): Unit = {
     /* TODO: optimize by giving writer parameter to toXML*/
diff --git a/shared/src/main/scala/scala/xml/dtd/DTD.scala b/shared/src/main/scala/scala/xml/dtd/DTD.scala
index 9b334a8dc..fd9c22bde 100644
--- a/shared/src/main/scala/scala/xml/dtd/DTD.scala
+++ b/shared/src/main/scala/scala/xml/dtd/DTD.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 package dtd
 
+import xml.Nullables._
 import scala.collection.mutable
 import scala.collection.Seq
 
@@ -23,7 +24,7 @@ import scala.collection.Seq
  *  @author Burak Emir
  */
 abstract class DTD {
-  var externalID: ExternalID = _
+  var externalID: Nullable[ExternalID] = _
   var decls: List[Decl] = Nil
   def notations: Seq[NotationDecl] = Nil
   def unparsedEntities: Seq[EntityDecl] = Nil
diff --git a/shared/src/main/scala/scala/xml/dtd/Decl.scala b/shared/src/main/scala/scala/xml/dtd/Decl.scala
index c2cf53e18..1965c4e9c 100644
--- a/shared/src/main/scala/scala/xml/dtd/Decl.scala
+++ b/shared/src/main/scala/scala/xml/dtd/Decl.scala
@@ -15,6 +15,7 @@ package xml
 package dtd
 
 import Utility.sbToString
+import xml.Nullables._
 
 /**
  * XML declarations
@@ -55,12 +56,12 @@ case class AttListDecl(name: String, attrs: List[AttrDecl]) extends MarkupDecl {
  *  versions might provide a way to access the attribute types more
  *  directly.
  */
-case class AttrDecl(name: String, tpe: String, default: DefaultDecl) {
+case class AttrDecl(name: String, tpe: String, default: Nullable[DefaultDecl]) {
   override def toString: String = sbToString(buildString)
 
   def buildString(sb: StringBuilder): StringBuilder = {
     sb.append(s"  $name $tpe ")
-    default.buildString(sb)
+    default.nn.buildString(sb)
   }
 }
 
diff --git a/shared/src/main/scala/scala/xml/dtd/ExternalID.scala b/shared/src/main/scala/scala/xml/dtd/ExternalID.scala
index 80b9da867..5913558f5 100644
--- a/shared/src/main/scala/scala/xml/dtd/ExternalID.scala
+++ b/shared/src/main/scala/scala/xml/dtd/ExternalID.scala
@@ -13,6 +13,7 @@
 package scala
 package xml
 package dtd
+import xml.Nullables._
 
 /**
  * an ExternalIDs - either PublicID or SystemID
@@ -20,8 +21,8 @@ package dtd
  *  @author Burak Emir
  */
 sealed abstract class ExternalID extends parsing.TokenTests {
-  def quoted(s: String): String = {
-    val c: Char = if (s.contains('"')) '\'' else '"'
+  def quoted(s: Nullable[String]): String = {
+    val c: Char = if (s.nn.contains('"')) '\'' else '"'
     s"$c$s$c"
   }
 
@@ -35,8 +36,8 @@ sealed abstract class ExternalID extends parsing.TokenTests {
   def buildString(sb: StringBuilder): StringBuilder =
     sb.append(this.toString)
 
-  def systemId: String
-  def publicId: String
+  def systemId: Nullable[String]
+  def publicId: Nullable[String]
 }
 
 /**
@@ -59,7 +60,7 @@ case class SystemID(override val systemId: String) extends ExternalID {
  *  @param  publicId the public identifier literal
  *  @param  systemId (can be null for notation pubIDs) the system identifier literal
  */
-case class PublicID(override val publicId: String, override val systemId: String) extends ExternalID {
+case class PublicID(override val publicId: String, override val systemId: Nullable[String]) extends ExternalID {
   if (!checkPubID(publicId))
     throw new IllegalArgumentException("publicId must consist of PubidChars")
 
@@ -82,8 +83,8 @@ case class PublicID(override val publicId: String, override val systemId: String
  *  @author Michael Bayne
  */
 object NoExternalID extends ExternalID {
-  override val publicId: ScalaVersionSpecificReturnTypes.NoExternalIDId = null
-  override val systemId: ScalaVersionSpecificReturnTypes.NoExternalIDId = null
+  override val publicId: Nullable[ScalaVersionSpecificReturnTypes.NoExternalIDId] = null
+  override val systemId: Nullable[ScalaVersionSpecificReturnTypes.NoExternalIDId] = null
 
   override def toString: String = ""
 }
diff --git a/shared/src/main/scala/scala/xml/include/CircularIncludeException.scala b/shared/src/main/scala/scala/xml/include/CircularIncludeException.scala
index ecff559df..0039a4473 100644
--- a/shared/src/main/scala/scala/xml/include/CircularIncludeException.scala
+++ b/shared/src/main/scala/scala/xml/include/CircularIncludeException.scala
@@ -14,11 +14,13 @@ package scala
 package xml
 package include
 
+import xml.Nullables._
+
 /**
  *  A `CircularIncludeException` is thrown when an included document attempts
  *  to include itself or one of its ancestor documents.
  */
-class CircularIncludeException(message: String) extends XIncludeException {
+class CircularIncludeException(message: Nullable[String]) extends XIncludeException {
 
   /**
    * Constructs a `CircularIncludeException` with `'''null'''`.
diff --git a/shared/src/main/scala/scala/xml/include/UnavailableResourceException.scala b/shared/src/main/scala/scala/xml/include/UnavailableResourceException.scala
index 7499a3f14..883ee8161 100644
--- a/shared/src/main/scala/scala/xml/include/UnavailableResourceException.scala
+++ b/shared/src/main/scala/scala/xml/include/UnavailableResourceException.scala
@@ -14,11 +14,13 @@ package scala
 package xml
 package include
 
+import xml.Nullables._
+
 /**
  * An `UnavailableResourceException` is thrown when an included document
  * cannot be found or loaded.
  */
-class UnavailableResourceException(message: String)
+class UnavailableResourceException(message: Nullable[String])
   extends XIncludeException(message) {
   def this() = this(null)
 }
diff --git a/shared/src/main/scala/scala/xml/include/XIncludeException.scala b/shared/src/main/scala/scala/xml/include/XIncludeException.scala
index 4d2a809cf..a8d4fe21a 100644
--- a/shared/src/main/scala/scala/xml/include/XIncludeException.scala
+++ b/shared/src/main/scala/scala/xml/include/XIncludeException.scala
@@ -14,6 +14,8 @@ package scala
 package xml
 package include
 
+import xml.Nullables._
+
 /**
  * `XIncludeException` is the generic superclass for all checked exceptions
  * that may be thrown as a result of a violation of XInclude's rules.
@@ -25,14 +27,14 @@ package include
  *
  * @param   message   the detail message.
  */
-class XIncludeException(message: String) extends Exception(message) {
+class XIncludeException(message: Nullable[String]) extends Exception(message) {
 
   /**
    * uses `'''null'''` as its error detail message.
    */
   def this() = this(null)
 
-  private var rootCause: Throwable = _
+  private var rootCause: Nullable[Throwable] = _
 
   /**
    * When an `IOException`, `MalformedURLException` or other generic
@@ -57,5 +59,5 @@ class XIncludeException(message: String) extends Exception(message) {
    * @return Throwable   the underlying exception which caused the
    *                     `XIncludeException` to be thrown
    */
-  def getRootCause: Throwable = this.rootCause
+  def getRootCause: Nullable[Throwable] = this.rootCause
 }
diff --git a/shared/src/main/scala/scala/xml/include/sax/EncodingHeuristics.scala b/shared/src/main/scala/scala/xml/include/sax/EncodingHeuristics.scala
index fe8b0e323..63f89b066 100644
--- a/shared/src/main/scala/scala/xml/include/sax/EncodingHeuristics.scala
+++ b/shared/src/main/scala/scala/xml/include/sax/EncodingHeuristics.scala
@@ -16,6 +16,7 @@ package include.sax
 
 import java.io.InputStream
 import scala.util.matching.Regex
+import xml.Nullables._
 
 /**
  * `EncodingHeuristics` reads from a stream
@@ -50,9 +51,9 @@ object EncodingHeuristics {
    * @return         the name of the encoding.
    */
   def readEncodingFromStream(in: InputStream): String = {
-    var ret: String = null
+    var ret: Nullable[String] = null
     val bytesToRead: Int = 1024 // enough to read most XML encoding declarations
-    def resetAndRet: String = { in.reset(); ret }
+    def resetAndRet: Nullable[String] = { in.reset(); ret }
 
     // This may fail if there are a lot of space characters before the end
     // of the encoding declaration
@@ -71,7 +72,7 @@ object EncodingHeuristics {
       case _                        => null
     }
     if (ret != null)
-      return resetAndRet
+      return resetAndRet.nn
 
     def readASCIIEncoding: String = {
       val data: Array[Byte] = new Array[Byte](bytesToRead - 4)
@@ -98,6 +99,6 @@ object EncodingHeuristics {
       case (0x4C, 0x6F, 0xA7, 0x94) => utf8 // XXX EBCDIC
       case _                        => utf8 // no XML or text declaration present
     }
-    resetAndRet
+    resetAndRet.nn
   }
 }
diff --git a/shared/src/main/scala/scala/xml/include/sax/XIncludeFilter.scala b/shared/src/main/scala/scala/xml/include/sax/XIncludeFilter.scala
index b82414d61..71c4df8bb 100644
--- a/shared/src/main/scala/scala/xml/include/sax/XIncludeFilter.scala
+++ b/shared/src/main/scala/scala/xml/include/sax/XIncludeFilter.scala
@@ -15,6 +15,7 @@ package xml
 package include.sax
 
 import scala.xml.include._
+import xml.Nullables._
 import org.xml.sax.{Attributes, Locator, XMLReader}
 import org.xml.sax.helpers.{AttributesImpl, NamespaceSupport, XMLFilterImpl, XMLReaderFactory}
 
@@ -250,7 +251,7 @@ class XIncludeFilter extends XMLFilterImpl {
   private def includeTextDocument(url: String, encoding1: String): Unit = {
     var encoding: String = encoding1
     if (encoding == null || encoding.trim.isEmpty) encoding = "UTF-8"
-    var source: URL = null
+    var source: Nullable[URL] = null
     try {
       val base: URL = bases.peek
       source = new URL(base, url)
@@ -262,7 +263,7 @@ class XIncludeFilter extends XMLFilterImpl {
     }
 
     try {
-      val uc: URLConnection = source.openConnection
+      val uc: URLConnection = source.nn.openConnection
       val in: BufferedInputStream = new BufferedInputStream(uc.getInputStream)
       val encodingFromHeader: String = uc.getContentEncoding
       var contentType: String = uc.getContentType
@@ -293,7 +294,7 @@ class XIncludeFilter extends XMLFilterImpl {
       case e: UnsupportedEncodingException =>
         throw new SAXException(s"Unsupported encoding: $encoding$getLocation", e)
       case e: IOException =>
-        throw new SAXException(s"Document not found: ${source.toExternalForm}$getLocation", e)
+        throw new SAXException(s"Document not found: ${source.nn.toExternalForm}$getLocation", e)
     }
   }
 
diff --git a/shared/src/main/scala/scala/xml/include/sax/XIncluder.scala b/shared/src/main/scala/scala/xml/include/sax/XIncluder.scala
index ec94be793..7b9809bde 100644
--- a/shared/src/main/scala/scala/xml/include/sax/XIncluder.scala
+++ b/shared/src/main/scala/scala/xml/include/sax/XIncluder.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 package include.sax
 
+import xml.Nullables._
 import org.xml.sax.{ ContentHandler, Locator, Attributes }
 import org.xml.sax.ext.LexicalHandler
 import java.io.{ OutputStream, OutputStreamWriter, IOException }
@@ -159,14 +160,14 @@ class XIncluder(outs: OutputStream, encoding: String) extends ContentHandler wit
 
   // Just need this reference so we can ask if a comment is
   // inside an include element or not
-  private var filter: XIncludeFilter = _
+  private var filter: Nullable[XIncludeFilter] = _
 
   def setFilter(filter: XIncludeFilter): Unit = {
     this.filter = filter
   }
 
   override def comment(ch: Array[Char], start: Int, length: Int): Unit = {
-    if (!inDTD && !filter.insideIncludeElement) {
+    if (!inDTD && !filter.nn.insideIncludeElement) {
       try {
         out.write("<!--")
         out.write(ch, start, length)
diff --git a/shared/src/main/scala/scala/xml/parsing/ConstructingHandler.scala b/shared/src/main/scala/scala/xml/parsing/ConstructingHandler.scala
index 226668219..e64825217 100755
--- a/shared/src/main/scala/scala/xml/parsing/ConstructingHandler.scala
+++ b/shared/src/main/scala/scala/xml/parsing/ConstructingHandler.scala
@@ -14,6 +14,8 @@ package scala
 package xml
 package parsing
 
+import xml.Nullables._
+
 /**
  * Implementation of MarkupHandler that constructs nodes.
  *
@@ -22,7 +24,7 @@ package parsing
 abstract class ConstructingHandler extends MarkupHandler {
   val preserveWS: Boolean
 
-  override def elem(pos: Int, pre: String, label: String, attrs: MetaData,
+  override def elem(pos: Int, pre: Nullable[String], label: String, attrs: MetaData,
            pscope: NamespaceBinding, empty: Boolean, nodes: NodeSeq): NodeSeq =
     Elem(pre, label, attrs, pscope, empty, nodes: _*)
 
diff --git a/shared/src/main/scala/scala/xml/parsing/DefaultMarkupHandler.scala b/shared/src/main/scala/scala/xml/parsing/DefaultMarkupHandler.scala
index 03ee009d0..3f65b99a1 100755
--- a/shared/src/main/scala/scala/xml/parsing/DefaultMarkupHandler.scala
+++ b/shared/src/main/scala/scala/xml/parsing/DefaultMarkupHandler.scala
@@ -14,10 +14,12 @@ package scala
 package xml
 package parsing
 
+import xml.Nullables._
+
 /** Default implementation of markup handler always returns `NodeSeq.Empty` */
 abstract class DefaultMarkupHandler extends MarkupHandler {
 
-  override def elem(pos: Int, pre: String, label: String, attrs: MetaData,
+  override def elem(pos: Int, pre: Nullable[String], label: String, attrs: MetaData,
            scope: NamespaceBinding, empty: Boolean, args: NodeSeq): NodeSeq = NodeSeq.Empty
 
   override def procInstr(pos: Int, target: String, txt: String): NodeSeq = NodeSeq.Empty
diff --git a/shared/src/main/scala/scala/xml/parsing/FactoryAdapter.scala b/shared/src/main/scala/scala/xml/parsing/FactoryAdapter.scala
index d3f75dd5c..57e9f4335 100644
--- a/shared/src/main/scala/scala/xml/parsing/FactoryAdapter.scala
+++ b/shared/src/main/scala/scala/xml/parsing/FactoryAdapter.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 package parsing
 
+import xml.Nullables._
 import scala.collection.Seq
 import org.xml.sax.{Attributes, Locator, SAXNotRecognizedException, SAXNotSupportedException}
 import org.xml.sax.ext.{DefaultHandler2, Locator2}
@@ -75,7 +76,7 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
     * 
     * @since 2.0.0 
     */
-  var hStack: List[Node] = List.empty // [ element ] contains siblings
+  var hStack: List[Nullable[Node]] = List.empty // [ element ] contains siblings
   /** List of element names
     * 
     * Previously was a mutable [[scala.collection.mutable.Stack Stack]], but is now a mutable reference to an immutable [[scala.collection.immutable.List List]].
@@ -158,7 +159,7 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
    * @param chIter
    * @return a new XML element.
    */
-  def createNode(pre: String, elemName: String, attribs: MetaData,
+  def createNode(pre: Nullable[String], elemName: String, attribs: MetaData,
                  scope: NamespaceBinding, chIter: List[Node]): Node // abstract
 
   /**
@@ -210,7 +211,7 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
 
   override def endDocument(): Unit = {
     // capture the epilogue at the end of the document
-    epilogue = hStack.init.reverse
+    epilogue = hStack.init.reverse.map(_.nn)
 
     val document = new Document
     this.document = Some(document)
@@ -246,14 +247,14 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
     hStack = hStack.last :: Nil // TODO List.empty
     scopeStack = scopeStack.tail // TODO List.empty
 
-    rootElem = null
+    rootElem = null.asInstanceOf[Node]
     prolog = List.empty
     epilogue = List.empty
 
     buffer.clear()
     inCDATA = false
     capture = false
-    curTag = null
+    curTag = null.asInstanceOf[String]
 
     attribStack = List.empty
     tagStack = List.empty
@@ -275,7 +276,7 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
 
     // capture the prolog at the start of the root element
     if (tagStack.isEmpty) {
-      prolog = hStack.reverse
+      prolog = hStack.reverse.asInstanceOf[List[Node]]
       hStack = List.empty
     }
 
@@ -295,13 +296,13 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
       val qname: String = attributes.getQName(i)
       val value: String = attributes.getValue(i)
       val (pre: Option[String], key: String) = Utility.splitName(qname)
-      def nullIfEmpty(s: String): String = if (s == "") null else s
+      def nullIfEmpty(s: String): Nullable[String] = if (s == "") null else s
 
       if (pre.contains("xmlns") || (pre.isEmpty && qname == "xmlns")) {
-        val arg: String = if (pre.isEmpty) null else key
+        val arg: Nullable[String] = if (pre.isEmpty) null else key
         scpe = NamespaceBinding(arg, nullIfEmpty(value), scpe)
       } else
-        m = Attribute(pre, key, Text(value), m)
+        m = Attribute(pre.orNull, key, Text(value), m)
     }
 
     // Add namespace bindings for the prefix mappings declared by this element
@@ -331,7 +332,7 @@ abstract class FactoryAdapter extends DefaultHandler2 with factory.XMLLoader[Nod
     attribStack = attribStack.tail
 
     // reverse order to get it right
-    val v: List[Node] = hStack.takeWhile(_ != null).reverse
+    val v: List[Node] = hStack.takeWhile(_ != null).reverse.asInstanceOf[List[Node]]
     hStack = hStack.dropWhile(_ != null) match {
       case null :: hs => hs
       case hs => hs
diff --git a/shared/src/main/scala/scala/xml/parsing/MarkupHandler.scala b/shared/src/main/scala/scala/xml/parsing/MarkupHandler.scala
index ab647cf76..69248fd52 100755
--- a/shared/src/main/scala/scala/xml/parsing/MarkupHandler.scala
+++ b/shared/src/main/scala/scala/xml/parsing/MarkupHandler.scala
@@ -17,6 +17,7 @@ package parsing
 import scala.collection.mutable
 import scala.io.Source
 import scala.xml.dtd._
+import xml.Nullables._
 
 /**
  * class that handles markup - provides callback methods to MarkupParser.
@@ -34,8 +35,8 @@ abstract class MarkupHandler {
   var decls: List[Decl] = Nil
   var ent: mutable.Map[String, EntityDecl] = new mutable.HashMap[String, EntityDecl]()
 
-  def lookupElemDecl(Label: String): ElemDecl =
-    (for (case z@ElemDecl(Label, _) <- decls) yield z).headOption.orNull
+  def lookupElemDecl(Label: String): Nullable[ElemDecl] =
+    (for (case z @ ElemDecl(Label, _) <- decls) yield z).headOption.orNull
 
   def replacementText(entityName: String): Source =
     Source.fromString(ent.get(entityName) match {
@@ -55,7 +56,7 @@ abstract class MarkupHandler {
    *  @param label    the local name
    *  @param attrs    the attributes (metadata)
    */
-  def elemStart(pos: Int, pre: String, label: String, attrs: MetaData, scope: NamespaceBinding): Unit = ()
+  def elemStart(pos: Int, pre: Nullable[String], label: String, attrs: MetaData, scope: NamespaceBinding): Unit = ()
 
   /**
    * callback method invoked by MarkupParser after end-tag of element.
@@ -64,7 +65,7 @@ abstract class MarkupHandler {
    *  @param pre      the prefix
    *  @param label    the local name
    */
-  def elemEnd(pos: Int, pre: String, label: String): Unit = ()
+  def elemEnd(pos: Int, pre: Nullable[String], label: String): Unit = ()
 
   /**
    * callback method invoked by MarkupParser after parsing an element,
@@ -77,7 +78,7 @@ abstract class MarkupHandler {
    *  @param empty    `true` if the element was previously empty; `false` otherwise.
    *  @param args     the children of this element
    */
-  def elem(pos: Int, pre: String, label: String, attrs: MetaData, scope: NamespaceBinding, empty: Boolean, args: NodeSeq): NodeSeq
+  def elem(pos: Int, pre: Nullable[String], label: String, attrs: MetaData, scope: NamespaceBinding, empty: Boolean, args: NodeSeq): NodeSeq
 
   /**
    * callback method invoked by MarkupParser after parsing PI.
diff --git a/shared/src/main/scala/scala/xml/parsing/MarkupParser.scala b/shared/src/main/scala/scala/xml/parsing/MarkupParser.scala
index 688ca3425..82d6ad5ab 100755
--- a/shared/src/main/scala/scala/xml/parsing/MarkupParser.scala
+++ b/shared/src/main/scala/scala/xml/parsing/MarkupParser.scala
@@ -14,6 +14,7 @@ package scala
 package xml
 package parsing
 
+import xml.Nullables._
 import scala.io.Source
 import scala.xml.dtd._
 import Utility.Escapes.{ pairs => unescape }
@@ -131,9 +132,9 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
   /** character buffer, for names */
   protected val cbuf: StringBuilder = new StringBuilder()
 
-  var dtd: DTD = _
+  var dtd: Nullable[DTD] = _
 
-  protected var doc: Document = _
+  protected var doc: Nullable[Document] = _
 
   override def eof: Boolean = { ch; reachedEof }
 
@@ -238,17 +239,17 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
     var info_prolog: (Option[String], Option[String], Option[Boolean]) = (None, None, None)
     if ('<' != ch) {
       reportSyntaxError("< expected")
-      return null
+      return null.asInstanceOf[Document]
     }
 
     nextch() // is prolog ?
-    var children: Seq[Node] = null
+    var children: Nullable[Seq[Node]] = null
     if ('?' == ch) {
       nextch()
       info_prolog = prolog()
-      doc.version = info_prolog._1
-      doc.encoding = info_prolog._2
-      doc.standAlone = info_prolog._3
+      doc.nn.version = info_prolog._1
+      doc.nn.encoding = info_prolog._2
+      doc.nn.standAlone = info_prolog._3
 
       children = content(TopScope) // DTD handled as side effect
     } else {
@@ -259,7 +260,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
     }
     //println("[MarkupParser::document] children now: "+children.toList)
     var elemCount: Int = 0
-    var theNode: Node = null
+    var theNode: Nullable[Node] = null
     for (c <- children) c match {
       case _: ProcInstr =>
       case _: Comment   =>
@@ -277,9 +278,9 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
       //Console.println(children.toList)
     }
 
-    doc.children = children
-    doc.docElem = theNode
-    doc
+    doc.nn.children = children
+    doc.nn.docElem = theNode.nn
+    doc.nn
   }
 
   /** append Unicode character to name buffer*/
@@ -521,7 +522,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
    *  }}}
    */
   def parseDTD(): Unit = { // dirty but fast
-    var extID: ExternalID = null
+    var extID: Nullable[ExternalID] = null
     if (dtd != null)
       reportSyntaxError("unexpected character (DOCTYPE already defined")
     xToken("DOCTYPE")
@@ -539,7 +540,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
 
     if ((null != extID) && isValidating) {
 
-      pushExternal(extID.systemId)
+      pushExternal(extID.systemId.nn)
       extIndex = inpStack.length
 
       extSubset()
@@ -562,7 +563,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
     }
     //this.dtd.initializeEntities();
     if (doc != null)
-      doc.dtd = this.dtd
+      doc.nn.dtd = this.dtd
 
     handle.endDTD(n)
   }
@@ -668,7 +669,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
   //
 
   def extSubset(): Unit = {
-    var textdecl: (Option[String], Option[String]) = null
+    var textdecl: Nullable[(Option[String], Option[String])] = null
     if (ch == '<') {
       nextch()
       if (ch == '?') {
@@ -834,7 +835,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
       val atpe: String = cbuf.toString
       cbuf.setLength(0)
 
-      val defdecl: DefaultDecl = ch match {
+      val defdecl: Nullable[DefaultDecl] = ch match {
         case '\'' | '"' =>
           DEFAULT(fixed = false, xAttributeValue())
 
@@ -927,7 +928,7 @@ trait MarkupParser extends MarkupParserCommon with TokenTests {
       xSpace()
       val pubID: String = pubidLiteral()
       xSpaceOpt()
-      val sysID: String = if (ch != '>')
+      val sysID: Nullable[String] = if (ch != '>')
         systemLiteral()
       else
         null
diff --git a/shared/src/main/scala/scala/xml/parsing/NoBindingFactoryAdapter.scala b/shared/src/main/scala/scala/xml/parsing/NoBindingFactoryAdapter.scala
index fcc522a6b..89cb00c7d 100644
--- a/shared/src/main/scala/scala/xml/parsing/NoBindingFactoryAdapter.scala
+++ b/shared/src/main/scala/scala/xml/parsing/NoBindingFactoryAdapter.scala
@@ -16,6 +16,7 @@ package parsing
 
 import scala.collection.Seq
 import factory.NodeFactory
+import xml.Nullables._
 
 /**
  * nobinding adaptor providing callbacks to parser to create elements.
@@ -31,7 +32,7 @@ class NoBindingFactoryAdapter extends FactoryAdapter with NodeFactory[Elem] {
 
   /** From FactoryAdapter.  Creates a node. never creates the same node twice, using hash-consing.
      TODO: deprecate as in Elem, or forward to create?? */
-  override def createNode(pre: String, label: String, attrs: MetaData, scope: NamespaceBinding, children: List[Node]): Elem =
+  override def createNode(pre: Nullable[String], label: String, attrs: MetaData, scope: NamespaceBinding, children: List[Node]): Elem =
     Elem(pre, label, attrs, scope, children.isEmpty, children: _*)
 
   /** Creates a text node. */
diff --git a/shared/src/test/scala/scala/xml/AttributeTest.scala b/shared/src/test/scala/scala/xml/AttributeTest.scala
index 90ea3b0a6..793d2af0c 100644
--- a/shared/src/test/scala/scala/xml/AttributeTest.scala
+++ b/shared/src/test/scala/scala/xml/AttributeTest.scala
@@ -1,6 +1,7 @@
 package scala.xml
 
 import scala.collection.Seq
+import xml.Nullables._
 import org.junit.Test
 import org.junit.Assert.assertEquals
 
@@ -16,7 +17,7 @@ class AttributeTest {
     val y: MetaData = x.remove("foo")
     assertEquals(Null, y)
 
-    val z: UnprefixedAttribute = new UnprefixedAttribute("foo", null:NodeSeq, x)
+    val z: UnprefixedAttribute = new UnprefixedAttribute("foo", null: Nullable[NodeSeq], x)
     assertEquals(None, z.get("foo"))
 
     var appended: MetaData = x.append(x).append(x).append(x)
diff --git a/shared/src/test/scala/scala/xml/MetaDataTest.scala b/shared/src/test/scala/scala/xml/MetaDataTest.scala
index 039382fad..9b25ef62a 100644
--- a/shared/src/test/scala/scala/xml/MetaDataTest.scala
+++ b/shared/src/test/scala/scala/xml/MetaDataTest.scala
@@ -2,13 +2,14 @@ package scala.xml
 
 import org.junit.Test
 import org.junit.Assert.assertEquals
+import xml.Nullables._
 
 class MetaDataTest {
 
   @Test
   def absentElementPrefixed1(): Unit = {
     // type ascription to help overload resolution pick the right variant
-    assertEquals(null: Object, Null("za://foo.com", TopScope, "bar"))
+    assertEquals(null: Nullable[Object], Null("za://foo.com", TopScope, "bar"))
     assertEquals(null, Null("bar"))
   }
 
@@ -43,8 +44,8 @@ class MetaDataTest {
   def attributeExtractor(): Unit = {
     def domatch(x: Node): Node = {
       x match {
-            case Node("foo", md @ UnprefixedAttribute(_, value, _), _*) if value.nonEmpty =>
-                 md("bar")(0)
+            case Node("foo", md @ UnprefixedAttribute(_, value, _), _*) if value.nn.nonEmpty =>
+                 md("bar").asInstanceOf[Seq[Node]](0)
             case _ => new Atom(3)
       }
     }
diff --git a/shared/src/test/scala/scala/xml/NodeSeqTest.scala b/shared/src/test/scala/scala/xml/NodeSeqTest.scala
index a5808e797..11158454e 100644
--- a/shared/src/test/scala/scala/xml/NodeSeqTest.scala
+++ b/shared/src/test/scala/scala/xml/NodeSeqTest.scala
@@ -5,6 +5,7 @@ import org.junit.Assert.assertEquals
 import org.junit.Assert.fail
 
 import scala.collection.immutable
+import xml.Nullables._
 
 class NodeSeqTest {
 
diff --git a/shared/src/test/scala/scala/xml/XMLTest.scala b/shared/src/test/scala/scala/xml/XMLTest.scala
index 746d58d68..fc781081d 100644
--- a/shared/src/test/scala/scala/xml/XMLTest.scala
+++ b/shared/src/test/scala/scala/xml/XMLTest.scala
@@ -9,6 +9,7 @@ import scala.collection.Iterable
 import scala.collection.Seq
 import scala.xml.dtd.{DocType, PublicID}
 import scala.xml.Utility.sort
+import xml.Nullables._
 
 object XMLTest {
   val e: MetaData = Null //Node.NoAttributes
@@ -400,9 +401,9 @@ Ours is the portal of hope, come as you are."
 
   @UnitTest
   def t5052(): Unit = {
-    assertTrue(<elem attr={ null: String }/> xml_== <elem/>)
+    assertTrue(<elem attr={ null: Nullable[String] }/> xml_== <elem/>)
     assertTrue(<elem attr={ None }/> xml_== <elem/>)
-    assertTrue(<elem/> xml_== <elem attr={ null: String }/>)
+    assertTrue(<elem/> xml_== <elem attr={ null: Nullable[String] }/>)
     assertTrue(<elem/> xml_== <elem attr={ None }/>)
   }
 
@@ -415,9 +416,9 @@ Ours is the portal of hope, come as you are."
     assertHonorsIterableContract(<a y={ None }/>.attributes)
     assertHonorsIterableContract(<a y={ None } x=""/>.attributes)
     assertHonorsIterableContract(<a a="" y={ None }/>.attributes)
-    assertHonorsIterableContract(<a y={ null: String }/>.attributes)
-    assertHonorsIterableContract(<a y={ null: String } x=""/>.attributes)
-    assertHonorsIterableContract(<a a="" y={ null: String }/>.attributes)
+    assertHonorsIterableContract(<a y={ null: Nullable[String] }/>.attributes)
+    assertHonorsIterableContract(<a y={ null: Nullable[String] } x=""/>.attributes)
+    assertHonorsIterableContract(<a a="" y={ null: Nullable[String] }/>.attributes)
   }
 
   @UnitTest
@@ -453,9 +454,9 @@ Ours is the portal of hope, come as you are."
   @UnitTest
   def attributes(): Unit = {
     val noAttr: Elem = <t/>
-    val attrNull: Elem = <t a={ null: String }/>
+    val attrNull: Elem = <t a={ null: Nullable[String] }/>
     val attrNone: Elem = <t a={ None: Option[Seq[Node]] }/>
-    val preAttrNull: Elem = <t p:a={ null: String }/>
+    val preAttrNull: Elem = <t p:a={ null: Nullable[String] }/>
     val preAttrNone: Elem = <t p:a={ None: Option[Seq[Node]] }/>
     assertEquals(noAttr, attrNull)
     assertEquals(noAttr, attrNone)
@@ -463,8 +464,8 @@ Ours is the portal of hope, come as you are."
     assertEquals(noAttr, preAttrNone)
 
     val xml1: Elem = <t b="1" d="2"/>
-    val xml2: Elem = <t a={ null: String } p:a={ null: String } b="1" c={ null: String } d="2"/>
-    val xml3: Elem = <t b="1" c={ null: String } d="2" a={ null: String } p:a={ null: String }/>
+    val xml2: Elem = <t a={ null: Nullable[String] } p:a={ null: Nullable[String] } b="1" c={ null: Nullable[String] } d="2"/>
+    val xml3: Elem = <t b="1" c={ null: Nullable[String] } d="2" a={ null: Nullable[String] } p:a={ null: Nullable[String] }/>
     assertEquals(xml1, xml2)
     assertEquals(xml1, xml3)