fix(admin): add default value for broker option (#6033)

* fix(admin): add default value for broker option

www/include/Administration/parameters/DB-Func.php

@@ -164,7 +164,12 @@ function updateNagiosConfigData($gopt_id = null)
         isset($ret["interval_length"]) && $ret["interval_length"] != null
             ? $pearDB->escape($ret["interval_length"]) : "NULL"
     );
-    updateOption($pearDB, "broker", $pearDB->escape($ret['broker']));
+    updateOption(
+        $pearDB,
+        "broker",
+        isset($ret["broker"]) && $ret["broker"] != null
+            ? $pearDB->escape($ret['broker']) : "broker"
+    );
     $pearDB->query("UPDATE acl_resources SET changed = 1");
     
     /*