Fix lints of two varieties: unnecessary_null_in_if_null_operators, type_init_formals (#1971)

Author: srawlins

lib/src/dartdoc_options.dart

@@ -1237,7 +1237,7 @@ abstract class _DartdocArgOption<T> implements DartdocOption<T> {
     } else if (_isInt || _isDouble || _isString) {
       argParser.addOption(argName,
           abbr: abbr,
-          defaultsTo: defaultsTo?.toString() ?? null,
+          defaultsTo: defaultsTo?.toString(),
           help: help,
           hide: hide);
     } else if (_isListString || _isMapString) {

lib/src/source_linker.dart

@@ -59,12 +59,12 @@ class SourceLinker {
   /// Most users of this class should use the [SourceLinker.fromElement] factory
   /// instead.  This constructor is public for testing.
   SourceLinker(
-      {List<String> this.excludes,
-      int this.lineNumber,
-      String this.sourceFileName,
-      String this.revision,
-      String this.root,
-      String this.uriTemplate}) {
+      {this.excludes,
+      this.lineNumber,
+      this.sourceFileName,
+      this.revision,
+      this.root,
+      this.uriTemplate}) {
     assert(excludes != null, 'linkToSource excludes can not be null');
     if (revision != null || root != null || uriTemplate != null) {
       if (root == null || uriTemplate == null) {