- Comparison made before transforming to string was skipping nulls and not nulls but empty

src/Repository.php

@@ -319,6 +319,10 @@ class Repository implements RepositoryInterface
                 }
             }
 
+            if (is_null($e1) || is_null($e2)) {
+                return $e1 !== $e2;
+            }
+
             return (string) $e1 !== (string) $e2;
         });
     }