diff --git a/interface.php b/interface.php
index 488517a..8b085da 100644
--- a/interface.php
+++ b/interface.php
@@ -512,7 +512,12 @@ function get_results_by_gameid(ReqHandler &$rh, array $params): array
         }
 
         // execute filtering
-        $game_results = $testMgr->getResultsByGameId($gameid, $filter, $ordering, true, $group_filter);
+        $game_results = null;
+        if ($group_filter !== []) {
+            $game_results = $testMgr->getResultsByGameId($gameid, $filter, $ordering, true, $group_filter);
+        } else {
+            $game_results = $testMgr->getResultsByGameId($gameid, $filter, $ordering, true);
+        }
         $result = $game_results;
     }