diff --git a/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php b/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php
index 672a5afa0..40b7f09d9 100644
--- a/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php
+++ b/lib/Doctrine/ORM/Persisters/BasicEntityPersister.php
@@ -1695,9 +1695,10 @@ class BasicEntityPersister
                 $idValues = $class->getIdentifierValues($value);
             }
 
-            if (array_key_exists(key($idValues), $idValues)){
-                $value = $idValues[key($idValues)];
-            }
+            $key = key($idValues);
+            if (null !== $key){
+                $value = $idValues[$key];
+           } 
         }
 
         return $value;