No "master" worker_id in session fixture

[andrewVolodko]

I want to perform the particular action only once per test run.
As mentioned here, it can be done by checking, that now it's a master worker.
https://pytest-xdist.readthedocs.io/en/latest/how-to.html#making-session-scoped-fixtures-execute-only-once

But there is no worker with id = "master".

Here is my code:

    @fixture(scope="session", autouse=True)
    def session_setup(self, worker_id):
        if worker_id == "master":
            print()

BTW, there is no master worker only when I'm running tests in parallel with flag -n 2 or more.