fix SonataAdminBundle #1099

Form/Type/ModelReferenceType.php

@@ -45,10 +45,19 @@ class ModelReferenceType extends AbstractType
         $resolver->setDefaults(array(
             'compound'      => false,
             'model_manager' => null,
-            'class'         => null
+            'class'         => null,
+            'parent'        => 'text'
         ));
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    public function getParent()
+    {
+        return 'text';
+    }
+
     /**
      * {@inheritDoc}
      */
@@ -56,4 +65,4 @@ class ModelReferenceType extends AbstractType
     {
         return 'sonata_type_model_reference';
     }
-}
+}