--- /dev/null
+++ ../Classes/Library/Configuration.php
@@ -376,6 +376,11 @@
         $ldapAttributes = [];
         if (is_array($mapping)) {
             foreach ($mapping as $field => $attribute) {
+                if (!is_string($field)) {
+                    // ignore clés numériques ou non-string
+                    continue;
+                }
+
                 if (str_ends_with($field, '.')) {
                     // This is a TypoScript configuration
                     continue;