Issue #3373779: Return value must be of type string, null returned

src/Services/AuditFilesConfig.php

@@ -27,7 +27,8 @@ final class AuditFilesConfig implements AuditFilesConfigInterface {
    * {@inheritdoc}
    */
   public function getFileSystemPath(): string {
-    return $this->configFactory->get('auditfiles.settings')->get('auditfiles_file_system_path');
+    $system_path = $this->configFactory->get('auditfiles.settings')->get('auditfiles_file_system_path');
+    return !empty($system_path) ? $system_path : '';
   }
 
   /**