diff --git a/src/Transformer/AbstractArrayTransformer.php b/src/Transformer/AbstractArrayTransformer.php
index 4e2f69ca..f29a3c8c 100644
--- a/src/Transformer/AbstractArrayTransformer.php
+++ b/src/Transformer/AbstractArrayTransformer.php
@@ -47,6 +47,15 @@ public function transform(Expr $input, Expr $target, PropertyMetadata $propertyM
         $existingValue = new Expr\Variable($uniqueVariableScope->getUniqueName('existingValue'));
         $assignByRef = $this->itemTransformer instanceof AssignedByReferenceTransformerInterface && $this->itemTransformer->assignByRef();
 
+        // Pre-compute $existingValue BEFORE the inner transformer is called: it consumes
+        // $existingValue (via withNewContext) and emitting the assignment afterwards
+        // produced "Undefined variable" warnings in PHP 8+.
+        if ($propertyMapping->target->readAccessor !== null && $this->itemTransformer instanceof IdentifierHashInterface) {
+            $hashValueTargetVariable = new Expr\Variable($uniqueVariableScope->getUniqueName('hashValueTarget'));
+            $itemStatements[] = new Stmt\Expression(new Expr\Assign($hashValueTargetVariable, $this->itemTransformer->getSourceHashExpression($loopValueVar)));
+            $itemStatements[] = new Stmt\Expression(new Expr\Assign($existingValue, new Expr\BinaryOp\Coalesce(new Expr\ArrayDimFetch($exisingValuesIndexed, $hashValueTargetVariable), new Expr\ConstFetch(new Name('null')))));
+        }
+
         /* Get the transform statements for the source property */
         [$output, $transformStatements] = $this->itemTransformer->transform($loopValueVar, $target, $propertyMapping, $uniqueVariableScope, $source, $existingValue);
 
@@ -89,12 +98,7 @@ public function transform(Expr $input, Expr $target, PropertyMetadata $propertyM
             }
 
             $mappedValueVar = new Expr\Variable($uniqueVariableScope->getUniqueName('mappedValue'));
-            $hashValueTargetVariable = new Expr\Variable($uniqueVariableScope->getUniqueName('hashValueTarget'));
 
-            if ($propertyMapping->target->readAccessor !== null && $this->itemTransformer instanceof IdentifierHashInterface) {
-                $itemStatements[] = new Stmt\Expression(new Expr\Assign($hashValueTargetVariable, $this->itemTransformer->getSourceHashExpression($loopValueVar)));
-                $itemStatements[] = new Stmt\Expression(new Expr\Assign($existingValue, new Expr\BinaryOp\Coalesce(new Expr\ArrayDimFetch($exisingValuesIndexed, $hashValueTargetVariable), new Expr\ConstFetch(new Name('null')))));
-            }
             $itemStatements[] = new Stmt\Expression(new Expr\Assign($mappedValueVar, $output));
             $itemStatements[] = new Stmt\If_(new Expr\BinaryOp\NotIdentical(new Expr\ConstFetch(new Name('null')), $mappedValueVar), [
                 'stmts' => [
@@ -132,10 +136,6 @@ public function transform(Expr $input, Expr $target, PropertyMetadata $propertyM
                         ]),
                     ],
                 ]);
-
-                $hashValueTargetVariable = new Expr\Variable($uniqueVariableScope->getUniqueName('hashValueTarget'));
-                $itemStatements[] = new Stmt\Expression(new Expr\Assign($hashValueTargetVariable, $this->itemTransformer->getSourceHashExpression($loopValueVar)));
-                $itemStatements[] = new Stmt\Expression(new Expr\Assign($existingValue, new Expr\BinaryOp\Coalesce(new Expr\ArrayDimFetch($exisingValuesIndexed, $hashValueTargetVariable), new Expr\ConstFetch(new Name('null')))));
             }
 
             $itemStatements[] = new Stmt\Expression($this->getAssignExpr($valuesVar, $output, $loopKeyVar, $assignByRef));
diff --git a/tests/AutoMapperTest/CollectionWithoutDeepPopulate/expected.data b/tests/AutoMapperTest/CollectionWithoutDeepPopulate/expected.data
new file mode 100644
index 00000000..edaf9e1a
--- /dev/null
+++ b/tests/AutoMapperTest/CollectionWithoutDeepPopulate/expected.data
@@ -0,0 +1,12 @@
+AutoMapper\Tests\AutoMapperTest\CollectionWithoutDeepPopulate\Target {
+  -items: [
+    AutoMapper\Tests\AutoMapperTest\CollectionWithoutDeepPopulate\TargetItem {
+      +id: 1
+      +label: "first"
+    }
+    AutoMapper\Tests\AutoMapperTest\CollectionWithoutDeepPopulate\TargetItem {
+      +id: 2
+      +label: "second"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/tests/AutoMapperTest/CollectionWithoutDeepPopulate/map.php b/tests/AutoMapperTest/CollectionWithoutDeepPopulate/map.php
new file mode 100644
index 00000000..4af41115
--- /dev/null
+++ b/tests/AutoMapperTest/CollectionWithoutDeepPopulate/map.php
@@ -0,0 +1,105 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Drop this file at:
+ *   tests/AutoMapperTest/CollectionWithoutDeepPopulate/map.php
+ *
+ * Then generate the expected dump:
+ *   UPDATE_FIXTURES=1 vendor/bin/phpunit --filter=testAutoMapperFixtures
+ *
+ * The fixture system in tests/AutoMapperTest.php::testAutoMapperFixtures
+ * picks it up automatically.
+ *
+ * Why it reproduces the bug:
+ *   - target has an adder/remover (addItem/removeItem) ->
+ *     AbstractArrayTransformer takes the `isAdderRemover()` branch
+ *   - source collection has 2 items -> the inner foreach body executes
+ *   - no `deep_target_to_populate` -> the existing target items are
+ *     not indexed, but $existingvalue is still read inside
+ *     withNewContext() before being assigned (root cause)
+ *
+ * On 10.2.0 / current main this raises:
+ *   Warning: Undefined variable $existingvalue
+ *
+ * After the patch the warning is gone and the dump matches expected.data.
+ *
+ * To catch the warning automatically in CI, set the PHPUnit config:
+ *   <phpunit failOnWarning="true" ...>
+ * (already the default in the repo's phpunit.xml.dist).
+ */
+
+namespace AutoMapper\Tests\AutoMapperTest\CollectionWithoutDeepPopulate;
+
+use AutoMapper\Attribute\MapFrom;
+use AutoMapper\Tests\AutoMapperBuilder;
+
+class SourceItem
+{
+    public int $id;
+    public string $label;
+}
+
+class Source
+{
+    /** @var SourceItem[] */
+    public array $items = [];
+}
+
+class TargetItem
+{
+    #[MapFrom(source: SourceItem::class, identifier: true)]
+    public int $id;
+
+    public string $label;
+}
+
+class Target
+{
+    /** @var TargetItem[] */
+    private array $items = [];
+
+    public function addItem(TargetItem $item): void
+    {
+        $this->items[] = $item;
+    }
+
+    public function removeItem(TargetItem $item): void
+    {
+        foreach ($this->items as $key => $existing) {
+            if ($existing->id === $item->id) {
+                unset($this->items[$key]);
+                $this->items = array_values($this->items);
+                return;
+            }
+        }
+    }
+
+    /** @return TargetItem[] */
+    public function getItems(): array
+    {
+        return $this->items;
+    }
+}
+
+return (function () {
+    $autoMapper = AutoMapperBuilder::buildAutoMapper(mapPrivatePropertiesAndMethod: true);
+
+    $source = new Source();
+
+    $a = new SourceItem();
+    $a->id = 1;
+    $a->label = 'first';
+
+    $b = new SourceItem();
+    $b->id = 2;
+    $b->label = 'second';
+
+    $source->items = [$a, $b];
+
+    // No `deep_target_to_populate` and no pre-existing target. Pre-patch:
+    // raises Warning: Undefined variable $existingvalue. Post-patch:
+    // clean mapping.
+    return $autoMapper->map($source, Target::class);
+})();