Make entity return check sensible in JsonApiListener::_getSingleEntity().

Author: kevindecapite

src/Listener/JsonApiListener.php

@@ -1084,7 +1084,7 @@ protected function _getSingleEntity(Subject $subject): ?EntityInterface
             return $subject->entities->first();
         }
 
-        return $subject->get('query') ? $subject->get('query')->first() : $subject->get('entity');
+        return $subject->entity ?? null;
     }
 
     /**

tests/TestCase/Listener/JsonApiListenerTest.php

@@ -840,7 +840,7 @@ public function testGetSingleEntity()
         $subject->entity = $entity;
         $this->setReflectionClassInstance($listener);
         $result = $this->callProtectedMethod('_getSingleEntity', [$subject], $listener);
-        $this->assertSame($subject->get('entity'), $result);
+        $this->assertSame($subject->entity, $result);
     }
 
     public function testGetSingleEntityForEmptyResultSet()