Device Became unavailable

[mac-zhou]

This issue is often mentioned by users.
There are several reasons:

1. bug
2. encode wrong
3. reply takes too long time
4. device's reply is null
5. timeout
6. session closed

most reasons are 4-6.
many users don’t care about timeout at all, they care about too many errors and unavailable.
so, i'm thinking about to keep device's old state, when 4-6 occurred.

[mac-zhou]

next veriosn will fix, when responses is null, keep last state.
the warn and error log will also output to locating the problem.

[civarson]

Is this the same thing?

Logger: homeassistant.helpers.entity
Source: custom_components/midea_ac/climate.py:129
Integration: midea_ac (documentation)
First occurred: 9:32:07 AM (1214 occurrences)
Last logged: 2:35:25 PM

Update for climate.office_mini_split fails
Traceback (most recent call last):
File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 446, in async_update_ha_state
await self.async_device_update()
File "/usr/src/homeassistant/homeassistant/helpers/entity.py", line 641, in async_device_update
raise exc
File "/config/custom_components/midea_ac/climate.py", line 129, in async_update
await self.hass.async_add_executor_job(self._device.apply)
File "/usr/local/lib/python3.9/concurrent/futures/thread.py", line 52, in run
result = self.fn(*self.args, **self.kwargs)
File "/usr/local/lib/python3.9/site-packages/msmart/device.py", line 264, in apply
self._send_cmd(cmd)
File "/usr/local/lib/python3.9/site-packages/msmart/device.py", line 208, in _send_cmd
responses = self._lan_service.appliance_transparent_send_8370(data)
File "/usr/local/lib/python3.9/site-packages/msmart/lan.py", line 136, in appliance_transparent_send_8370
data = self.security.encode_8370(data, msgtype)
File "/usr/local/lib/python3.9/site-packages/msmart/security.py", line 117, in encode_8370
data = self.aes_cbc_encrypt(data, self._tcp_key) + sign
File "/usr/local/lib/python3.9/site-packages/msmart/security.py", line 57, in aes_cbc_encrypt
return AES.new(key, AES.MODE_CBC, iv=self.iv).encrypt(raw)
File "/usr/local/lib/python3.9/site-packages/Cryptodome/Cipher/AES.py", line 232, in new
return _create_cipher(sys.modules[name], key, mode, *args, **kwargs)
File "/usr/local/lib/python3.9/site-packages/Cryptodome/Cipher/init.py", line 79, in _create_cipher
return modes[mode](factory, **kwargs)
File "/usr/local/lib/python3.9/site-packages/Cryptodome/Cipher/_mode_cbc.py", line 274, in _create_cbc_cipher
cipher_state = factory._create_base_cipher(kwargs)
File "/usr/local/lib/python3.9/site-packages/Cryptodome/Cipher/AES.py", line 92, in _create_base_cipher
if len(key) not in key_size:
TypeError: object of type 'NoneType' has no len()