Issue #2892205 by mikeker: Notice: Undefined index: bef when BEF is enabled...

Issue #2892205 by mikeker: Notice: Undefined index: bef when BEF is enabled while a view is being edited

src/Plugin/views/exposed_form/BetterExposedFilters.php

@@ -1478,7 +1478,10 @@ Title Desc|Z -> A</pre> Leave the replacement text blank to remove an option alt
     // Update legacy settings in the exposed form settings form. This
     // keep us from losing settings when an option is put into an
     // 'advanced options' details element.
-    $current = $this->updateLegacySettings($this->options['bef']);
+    $current = [];
+    if (isset($this->options['bef'])) {
+      $current = $this->updateLegacySettings($this->options['bef']);
+    }
 
     // Collect existing values or use defaults.
     $settings = $this->setDefaults($defaults, $current);