diff --git a/lib/classes/JsonApi/Routes/Blubber/FilterTrait.php b/lib/classes/JsonApi/Routes/Blubber/FilterTrait.php
index 40bf4b0a098ce56887950cd5734a8810f5d769a3..2d74f9c63c8ef8179f29b8ea2aa33f61cd467bc9 100644
--- a/lib/classes/JsonApi/Routes/Blubber/FilterTrait.php
+++ b/lib/classes/JsonApi/Routes/Blubber/FilterTrait.php
@@ -27,8 +27,8 @@ trait FilterTrait
     {
         $filtering = $this->getQueryParameters()->getFilteringParameters() ?? [];
 
-        $filters['since'] = $filtering['since'] ? self::fromISO8601($filtering['since'])->getTimestamp() : null;
-        $filters['before'] = $filtering['before'] ? self::fromISO8601($filtering['before'])->getTimestamp() : null;
+        $filters['since'] = isset($filtering['since']) ? self::fromISO8601($filtering['since'])->getTimestamp() : null;
+        $filters['before'] = isset($filtering['before']) ? self::fromISO8601($filtering['before'])->getTimestamp() : null;
         $filters['search'] = $filtering['search'] ?? null;
 
         return $filters;