validation problem shouldn't be reported as an error

frontend-js/src/main/js/GuiConnector.js

@@ -402,7 +402,7 @@ GuiConnector.prototype.alert = function (error, redirectIfSecurityError) {
  * @returns {Object}
  */
 GuiConnector.prototype.getErrorMessageForError = function (error) {
-  var expectedError = typeof error === 'string' || error instanceof SecurityError;
+  var expectedError = typeof error === 'string' || error instanceof SecurityError || error instanceof ValidationError;
   var errorData = {
     showReport: !expectedError,
     message: typeof error === 'string' ? error : error.message,