From b9d1cca9f40255ef83495b118f35c6d35eaee8de Mon Sep 17 00:00:00 2001
From: Jan-Hendrik Willms <tleilax+studip@gmail.com>
Date: Thu, 23 Mar 2023 07:40:34 +0000
Subject: [PATCH] do not accept strings as callables, fixes #2424

Closes #2424

Merge request studip/studip!1620
---
 lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php b/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php
index 42a5842edbe..45dc29d00dc 100644
--- a/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php
+++ b/lib/classes/JsonApi/JsonApiIntegration/FieldsetFilter.php
@@ -36,7 +36,7 @@ class FieldsetFilter extends \Neomerx\JsonApi\Representation\FieldSetFilter
      */
     private function resolveValue($value)
     {
-        if (is_callable($value)) {
+        if (!is_string($value) && is_callable($value)) {
             return $value();
         }
 
-- 
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