Error not specifiying any worker version for lines

https://gitlab.com/teklia/workers/pylaia/-/merge_requests/49/diffs#9962f69a58fba98783f606ffd906874a8dbfd603 introduced a new parameter to filter lines by worker_version_id. However, the default value is not well handled.

We need to do something like "" or None to disable filtering when no worker_version is given.