v2.9.0 is causing homebridge docker to crash repeatedly
### Describe the Bug

After updating the plugin, I get repeated crashes until downgrading. 

### To Reproduce

Start homebridge. Downgrading will fix the issue.

### Expected Behavior

Homebridge to start and remain running

### Relevant Log Output

```shell
[9/19/2023, 3:47:21 PM] [@switchbot/homebridge-switchbot] This plugin generated a warning from the characteristic 'Firmware Revision': characteristic was supplied illegal value: number instead of string, supplying illegal values will throw errors in the future. See https://homebridge.io/w/JtMGR for more info.
[9/19/2023, 3:47:21 PM] [@switchbot/homebridge-switchbot] This plugin generated a warning from the characteristic 'Firmware Revision': characteristic was supplied illegal value: number instead of string, supplying illegal values will throw errors in the future. See https://homebridge.io/w/JtMGR for more info.
[9/19/2023, 3:47:21 PM] TypeError: Cannot read properties of undefined (reading 'updateCharacteristic')
    at BlindTilt.updateHomeKitCharacteristics (/homebridge/node_modules/@switchbot/homebridge-switchbot/src/device/blindtilt.ts:911:34)
    at processTicksAndRejections (node:internal/process/task_queues:95:5)
[9/19/2023, 3:47:21 PM] Got SIGTERM, shutting down Homebridge...
[9/19/2023, 3:47:21 PM] [Meross] [Outdoor Switch] mqtt connection closed.
[9/19/2023, 3:47:21 PM] Got SIGTERM, shutting down child bridge process...
```


### Config for homebridge-switchbot

```shell
{
            "name": "SwitchBot",
            "credentials": {
                "token": "XXXXXXXXXXXXXXX",
                "secret": "XXXXXXXXXXXXXXXXXX",
                "notice": "Keep your Token & Secret a secret!"
            },
            "options": {
                "devices": [
                    {
                        "deviceId": "XXXXXXXXXXXXXXXXX",
                        "configDeviceType": "Blind Tilt",
                        "connectionType": "OpenAPI",
                        "blindTilt": {
                            "set_minStep": 5
                        }
                    }
                ]
            },
            "platform": "SwitchBot"
        },
```


### Screenshots

_No response_

### Device and Model

Blind Tilt and Hub Mini

### Node.js Version

v18.16.0

### NPM Version

?

### Homebridge Version

v1.6.1

### Homebridge Switchbot Plugin Version

v2.9.0

### Homebridge Config UI X Plugin Version

v4.50.5

### Operating System

Docker