[BUGFIX] Fix RecordService->getSingle return type

This fixes the case where reset([]) returned FALSE, but should
return NULL to match the method signature doc comments.

Classes/Service/RecordService.php

@@ -71,7 +71,7 @@ public function getSingle($table, $fields, $uid)
             ->where(sprintf('uid = %d', $uid))
             ->execute()
             ->fetchAll() ?: [];
-        return reset($results);
+        return reset($results) ?: null;
     }
 
     /**