Resolve #3479757 "Migration error undefined"

Closes #3479757

entityreference_migration.module

@@ -286,6 +286,9 @@ function _entityreference_migration_references_field_to_entityreference_field_cr
       'handler' => 'base',
       'handler_settings' => array (
         'target_bundles' => $target_bundles,
+        'sort' => array(
+          'type' => 'none',
+        ),
       ),
       'handler_submit' => 'Change handler',
       'target_type' => $target_type,