Issue #2936892 by matthieuscarset, CbStuart, rlhawk: Undefined index #options...

Issue #2936892 by matthieuscarset, CbStuart, rlhawk: Undefined index #options when $form['sort_order'] is exposed as Radios

src/Plugin/views/exposed_form/BetterExposedFilters.php

@@ -767,12 +767,14 @@ Title Desc|Z -> A</pre> Leave the replacement text blank to remove an option alt
         // Leave sort_by and sort_order as separate elements.
         if ('bef' == $settings['sort']['bef_format']) {
           foreach (['sort_by', 'sort_order'] as $field) {
-            $form[$field]['#theme'] = 'bef_radios';
-            $form[$field]['#type'] = 'radios';
-            if (empty($form[$field]['#process'])) {
-              $form[$field]['#process'] = array();
+            if (!empty($form[$field])) {
+              $form[$field]['#theme'] = 'bef_radios';
+              $form[$field]['#type'] = 'radios';
+              if (empty($form[$field]['#process'])) {
+                $form[$field]['#process'] = array();
+              }
+              $form[$field]['#process'][] = ['\Drupal\Core\Render\Element\Radios', 'processRadios'];
             }
-            $form[$field]['#process'][] = ['\Drupal\Core\Render\Element\Radios', 'processRadios'];
           }
         }
         elseif ('bef_links' == $settings['sort']['bef_format']) {