fix

rules-tests/CodeQuality/Rector/Identical/FlipTypeControlToUseExclusiveTypeRector/Fixture/on_assign.php.inc

@@ -0,0 +1,35 @@
+<?php
+
+namespace Rector\Tests\CodeQuality\Rector\Identical\FlipTypeControlToUseExclusiveTypeRector\Fixture;
+
+class OnAssign
+{
+    public function run(?\DateTimeImmutable $param)
+    {
+        if (null === ($paramValue = $param)) {
+            return 'no';
+        }
+
+        return $paramValue;
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\CodeQuality\Rector\Identical\FlipTypeControlToUseExclusiveTypeRector\Fixture;
+
+class OnAssign
+{
+    public function run(?\DateTimeImmutable $param)
+    {
+        if (!($paramValue = $param) instanceof \DateTimeImmutable) {
+            return 'no';
+        }
+
+        return $paramValue;
+    }
+}
+
+?>

rules/CodeQuality/Rector/Identical/FlipTypeControlToUseExclusiveTypeRector.php

@@ -6,7 +6,6 @@
 
 use PhpParser\Node;
 use PhpParser\Node\Expr;
-use PhpParser\Node\Expr\Assign;
 use PhpParser\Node\Expr\BinaryOp\Identical;
 use PhpParser\Node\Expr\BinaryOp\NotIdentical;
 use PhpParser\Node\Expr\BooleanNot;
@@ -87,11 +86,7 @@ private function processConvertToExclusiveType(
         ObjectType $objectType,
         Expr $expr,
         Identical|NotIdentical $binaryOp
-    ): BooleanNot|Instanceof_|null {
-        if ($expr instanceof Assign) {
-            return null;
-        }
-
+    ): BooleanNot|Instanceof_ {
         $fullyQualifiedType = $objectType instanceof ShortenedObjectType || $objectType instanceof AliasedObjectType
             ? $objectType->getFullyQualifiedName()
             : $objectType->getClassName();