RFLink refactor bug with 'wait_for_ack: false'

[javicalle]

Home Assistant release with the issue:

v0.81.0

Last working Home Assistant release (if known):
v0.80.3 (before RFLink refactor)

Operating environment (Hass.io/Docker/Windows/etc.):

HASSIO 1.4.0

Component/platform:

RFLink platform (detected in switch and cover components)

Description of problem:
After the RFLink platform refactor (my thanks to @emontnemery and @MartinHjelmare for the effort) my logs are showing a error trace every time I run an HA command:

2018-10-27 15:32:44 DEBUG (MainThread) [homeassistant.components.rflink] Sending command: on to Rflink device: eurodomest_0c66f3_01
2018-10-27 15:32:44 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
AttributeError: 'NoneType' object has no attribute 'send'
.../...
2018-10-27 16:04:58 DEBUG (MainThread) [homeassistant.components.cover.rflink] set_position :: command open_cover
2018-10-27 16:04:58 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
AttributeError: 'NoneType' object has no attribute 'send'

It seems that all commands are running fine with no problem, but some kind of exception is arrising.

After some research I have found that problem it's related with the rflink config attribute 'wait_for_ack: false' and '_async_send_command' method (components/rflink.py).

Also I have benn researching the code, but my knowledge can't deal with it.

Before refactor (only relevant part):

    async def _async_send_command(self, cmd, repetitions):
        .../...
        else:
            # Puts command on outgoing buffer and returns straight away.
            # Rflink protocol/transport handles asynchronous writing of buffer
            # to serial/tcp device. Does not wait for command send
            # confirmation.
            self.hass.async_add_job(ft.partial(
                self._protocol.send_command, self._device_id, cmd))
        .../...

After:

    async def _async_send_command(self, cmd, repetitions):
        .../...
        else:
            # Puts command on outgoing buffer and returns straight away.
            # Rflink protocol/transport handles asynchronous writing of buffer
            # to serial/tcp device. Does not wait for command send
            # confirmation.
            self.hass.async_create_task(self._protocol.send_command(
                self._device_id, cmd))
        .../...

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

rflink:
  port: /dev/ttyUSB0
  wait_for_ack: false

Traceback (if applicable):

Additional information:

[MartinHjelmare]

We should not create a task but just call the self._protocol.send_command method. It's a callback.