websocket race condition

https://gitlab.esrf.fr/workflow/ewoks/ewoksserver/-/jobs/574237

self = <ewoksserver.events.websocket.EwoksEventEmitter object at 0x00000146BEC255E0>
timeout = 3
    def stop(self, timeout: float = None):
        if self._thread is None:
            return
        self._stop_event.set()
>       self._thread.join(timeout=timeout)
E       AttributeError: 'NoneType' object has no attribute 'join'
..\build_venv\lib\site-packages\ewoksserver\events\websocket.py:84: AttributeError