'Test if service call create log book entry without message.'

def test_service_call_create_log_book_entry_no_message(self):

    calls = []
    @ha.callback
    def event_listener(event):
        'Append    on    event.'
        calls.append(event)
    self.hass.bus.listen(logbook.EVENT_LOGBOOK_ENTRY, event_listener)
    self.hass.services.call(logbook.DOMAIN, 'log', {}, True)
    self.hass.block_till_done()
    self.assertEqual(0, len(calls))
