[Bug]: 5.15.5: `Cannot serialize non-str key None`

### Describe the bug Upgraded from 5.15.4 to 5.15.5 and the integration is failing to load. Logs different from other reported bugs. ### To Reproduce update integration to 5.15.5 and restart HA. ### Expected behavior Expected update to work. ### Screenshots _No response_ ### Home Assistant Version 2026.6.4 ### Alexa Media Player Version 5.15.5 ### Alexa Media Player API library Version Not sure ### Have you entered a 52-character key for Amazon 2SV via Authenticator App login? Yes ### Is the HA core integration Alexa Devices installed? Yes ### Amazon Domain amazon.com (US) ### Amazon Domain (if Other) _No response_ ### Debug Logs (alexa_media & alexapy) ```text 2026-06-26 07:30:07.313 WARNING (MainThread) [custom_components.alexa_media] a******a@y*******m: last_called probe API TypeError (PUSH_EQUALIZER_STATE_CHANGE): Cannot serialize non-str key None File "/config/custom_components/alexa_media/__init__.py", line 1626, in _last_called_probe_worker 2026-06-26 07:30:17.836 WARNING (MainThread) [custom_components.alexa_media] a******a@y*******m: last_called probe API TypeError (PUSH_EQUALIZER_STATE_CHANGE): Cannot serialize non-str key None File "/config/custom_components/alexa_media/__init__.py", line 1626, in _last_called_probe_worker 2026-06-26 07:30:28.494 WARNING (MainThread) [custom_components.alexa_media] a******a@y*******m: last_called probe API TypeError (PUSH_EQUALIZER_STATE_CHANGE): Cannot serialize non-str key None File "/config/custom_components/alexa_media/__init__.py", line 1626, in _last_called_probe_worker 2026-06-26 07:30:39.027 WARNING (MainThread) [custom_components.alexa_media] a******a@y*******m: last_called probe API TypeError (PUSH_EQUALIZER_STATE_CHANGE): Cannot serialize non-str key None File "/config/custom_components/alexa_media/__init__.py", line 1626, in _last_called_probe_worker 2026-06-26 07:30:49.586 WARNING (MainThread) [custom_components.alexa_media] a******a@y*******m: last_called probe API TypeError (PUSH_EQUALIZER_STATE_CHANGE): Cannot serialize non-str key None File "/config/custom_components/alexa_media/__init__.py", line 1626, in _last_called_probe_worker 2026-06-26 07:31:00.166 WARNING (MainThread) [custom_components.alexa_media] a******a@y*******m: last_called probe API TypeError (PUSH_EQUALIZER_STATE_CHANGE): Cannot serialize non-str key None File "/config/custom_components/alexa_media/__init__.py", line 1626, in _last_called_probe_worker ``` ### Additional context _No response_