Line 35 checks if `$clientData['client_secret']` is not set and throws an error, while this line checks if it is empty. On `password` request grant types, you will not pass the `client_secret` at all, meaning line 35 will kick in. I think you should likely do a check for `isset($clientData['client_id'])` by itself on line 35, and then change this line to:

```php
if (!isset($clientData['client_secret'] || $clientData['client_secret'] == '') {
```