When I try to get the project's members from the API, without supplying a username_query (I want to get all members), the result from the client is empty. When I call the URL (https://gitlab.com/api/v4/projects/[projectID]/members) manually, I get all members. When I do supply a username_query I do get the users that comply to that query.

So something seems to be not working correctly.

Code without query:

$members = $client->projects()->members($projectId);
// $members is now an empty array

Code with query:

$members = $client->projects()->members($projectId, 'willem');
// $members now contains one member: me