Fatal error: Uncaught Error: Class "JsonSchema\Uri\Retrievers\AbstractRetriever" not found in /opt/lampp/htdocs/forum/flarum/vendor/justinrainbow/json-schema/src/JsonSchema/Uri/Retrievers/FileGetContents.php:19 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/forum/flarum/vendor/justinrainbow/json-schema/src/JsonSchema/Uri/Retrievers/FileGetContents.php on line 19