Homebridge beta 1.3.0-beta.67: characteristic was supplied illegal value: null!
# Bug Report

### Describe the Bug
Using the latest beta the ring plugin throws warnings around illegal values that homekit will reject.

### To Reproduce
Install beta 67 and restart homebridge

### Expected behavior
These errors should not occur.


### Screenshots/Logs
```
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
[18/02/2021, 10:50:27] [homebridge-ring] This plugin generated a warning from the characteristic 'Selected RTP Stream Configuration': characteristic was supplied illegal value: null! Home App will reject null for Apple defined characteristics See https://git.io/JtMGR for more info.
```

### Environment
<!-- ✍️edit: -->
 - OS: Raspbian
 - Node.js: v14.15.5
 - NPM: v6.14.11 
 - homebridge-ring: v9.15.1
 - homebridge: v1.3.0-beta.67 
