diff --git a/libraries/tbl_relation.lib.php b/libraries/tbl_relation.lib.php
index 60b020ed47..bc9bfe9243 100644
--- a/libraries/tbl_relation.lib.php
+++ b/libraries/tbl_relation.lib.php
@@ -159,14 +159,14 @@ function PMA_generateRelationalDropdown(
 /**
  * Function to get html for the common form
  *
- * @param string $db                 current database
- * @param string $table              current table
- * @param array  $columns            columns
- * @param array  $cfgRelation        configuration relation
- * @param string $tbl_storage_engine table storage engine
- * @param array  $existrel           db, table, column
- * @param array  $existrel_foreign   db, table, column
- * @param array  $options_array      options array
+ * @param string     $db                 current database
+ * @param string     $table              current table
+ * @param array      $columns            columns
+ * @param array      $cfgRelation        configuration relation
+ * @param string     $tbl_storage_engine table storage engine
+ * @param array|null $existrel           db, table, column
+ * @param array|null $existrel_foreign   db, table, column
+ * @param array      $options_array      options array
  *
  * @return string
  */
diff --git a/tbl_relation.php b/tbl_relation.php
index 9be5f6260c..e8af9d5407 100644
--- a/tbl_relation.php
+++ b/tbl_relation.php
@@ -148,7 +148,8 @@ $columns = $GLOBALS['dbi']->getColumns($db, $table);
 
 // common form
 $html_output .= PMA_getHtmlForCommonForm(
-    $db, $table, $columns, $cfgRelation, $tbl_storage_engine, $existrel,
+    $db, $table, $columns, $cfgRelation, $tbl_storage_engine,
+    isset($existrel) ? $existrel : null,
     isset($existrel_foreign) ? $existrel_foreign : null, $options_array
 );