re-adding method_exists

Author: weaverryan

src/Autocomplete/src/AutocompleteResultsExecutor.php

@@ -71,7 +71,7 @@ public function fetchResults(EntityAutocompleterInterface $autocompleter, string
 
         $results = [];
 
-        if (null === $groupBy = $autocompleter->getGroupBy()) {
+        if (!method_exists($autocompleter, 'getGroupBy') || null === $groupBy = $autocompleter->getGroupBy()) {
             foreach ($paginator as $entity) {
                 $results[] = [
                     'value' => $autocompleter->getValue($entity),