does not support number for ID

ID can be string, number, or null. Number does not seem to be supported.

```
jsonrpc-plugin-854987fc66-mt9n9 main 127.0.0.1 - - [19/Feb/2021 05:15:01] code 400, message Bad request syntax ('{"method":"init","params":[{}],"id":0}')
jsonrpc-plugin-854987fc66-mt9n9 main 127.0.0.1 - - [19/Feb/2021 05:15:01] "{"method":"init","params":[{}],"id":0}" 400 -
```