Fix error for html client response handling

frontend/src/helpers/HtmlClient.js

@@ -61,7 +61,7 @@ class HtmlClient {
 
     onError(error) {
         const response = error.response;
-        if (response.data) {
+        if (response && response.data && response.data.code) {
             switch (response.data.code) {
                 case 'rest_missing_callback_param':
                     store.dispatch(updateMessages([{code:'error', message: response.data.message }]));