diff --git a/api/src/Storage/Merge.php b/api/src/Storage/Merge.php
index 0e11c62b96..8c72092f50 100644
--- a/api/src/Storage/Merge.php
+++ b/api/src/Storage/Merge.php
@@ -1446,7 +1446,7 @@ abstract class Merge
 	 * @param string $content
 	 * @return array
 	 */
-	protected function get_app_replacements($app, $id, $content, $prefix)
+	protected function get_app_replacements($app, $id, $content, $prefix='')
 	{
 		$replacements = array();
 		if($app == 'addressbook')