diff --git a/admin/tool/xmldb/actions/edit_field_save/edit_field_save.class.php b/admin/tool/xmldb/actions/edit_field_save/edit_field_save.class.php
index 40bbeee44c910..ca9840edb130c 100644
--- a/admin/tool/xmldb/actions/edit_field_save/edit_field_save.class.php
+++ b/admin/tool/xmldb/actions/edit_field_save/edit_field_save.class.php
@@ -91,11 +91,11 @@ function invoke() {
         $comment = trim($comment);
 
         $type       = required_param('type', PARAM_INT);
-        $length     = strtolower(optional_param('length', NULL, PARAM_ALPHANUM));
+        $length     = strtolower(optional_param('length', '', PARAM_ALPHANUM));
         $decimals   = optional_param('decimals', NULL, PARAM_INT);
         $notnull    = optional_param('notnull', false, PARAM_BOOL);
         $sequence   = optional_param('sequence', false, PARAM_BOOL);
-        $default    = optional_param('default', NULL, PARAM_PATH);
+        $default    = optional_param('default', '', PARAM_PATH);
         $default    = trim($default);
 
         $editeddir = $XMLDB->editeddirs[$dirpath];
@@ -272,4 +272,3 @@ function invoke() {
         return $result;
     }
 }
-