add assign to variable fixture

rules-tests/TypeDeclaration/Rector/ClassMethod/ReturnTypeFromReturnNewRector/Fixture/assigned_to_variable.php.inc

@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\TypeDeclaration\Rector\ClassMethod\ReturnTypeFromReturnNewRector\Fixture;
+
+use Rector\Tests\TypeDeclaration\Rector\ClassMethod\ReturnTypeFromReturnNewRector\Source\SomeResponse;
+
+final class AssignedToVariable
+{
+    public function action()
+    {
+        $response = new SomeResponse();
+
+        return $response;
+    }
+}
+
+?>
+-----
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\TypeDeclaration\Rector\ClassMethod\ReturnTypeFromReturnNewRector\Fixture;
+
+use Rector\Tests\TypeDeclaration\Rector\ClassMethod\ReturnTypeFromReturnNewRector\Source\SomeResponse;
+
+final class AssignedToVariable
+{
+    public function action(): \Rector\Tests\TypeDeclaration\Rector\ClassMethod\ReturnTypeFromReturnNewRector\Source\SomeResponse
+    {
+        $response = new SomeResponse();
+
+        return $response;
+    }
+}
+
+?>

rules/TypeDeclaration/Rector/ClassMethod/ReturnTypeFromReturnNewRector.php

@@ -110,7 +110,13 @@ public function refactor(Node $node): ?Node
         }
 
         $returnType = $this->typeFactory->createMixedPassedOrUnionType($newTypes);
-        $node->returnType = $this->staticTypeMapper->mapPHPStanTypeToPhpParserNode($returnType, TypeKind::RETURN);
+
+        $returnTypeNode = $this->staticTypeMapper->mapPHPStanTypeToPhpParserNode($returnType, TypeKind::RETURN);
+        if (! $returnTypeNode instanceof \PhpParser\Node) {
+            return null;
+        }
+
+        $node->returnType = $returnTypeNode;
 
         return $node;
     }