diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a1aa885c09a96f702c9aade36e48753636e64b2e..0fb6f732f7187e1a39d25fb8755da46ddec588a8 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,4 +1,4 @@
-image: studip/studip:tests
+image: studip/studip:tests-php7.2
 
 variables:
   MYSQL_RANDOM_ROOT_PASSWORD: "true"
diff --git a/lib/classes/JsonApi/Routes/Files/FileRefsCreate.php b/lib/classes/JsonApi/Routes/Files/FileRefsCreate.php
index 940e197b154102d012b0633aa0186dbda4ede29c..e878c4925e1181a646133890892018ea2ea7c055 100644
--- a/lib/classes/JsonApi/Routes/Files/FileRefsCreate.php
+++ b/lib/classes/JsonApi/Routes/Files/FileRefsCreate.php
@@ -14,7 +14,10 @@ use JsonApi\Schemas\File as FileSchema;
 
 class FileRefsCreate extends JsonApiController
 {
-    use RangeHelperTrait, RoutesHelperTrait, ValidationTrait;
+    use RangeHelperTrait, RoutesHelperTrait, ValidationTrait {
+        ValidationTrait::arrayGet insteadof RoutesHelperTrait;
+        ValidationTrait::arrayHas insteadof RoutesHelperTrait;
+    }
 
     /**
      * @SuppressWarnings(PHPMD.UnusedFormalParameters)