How to clear value from the device state

[grafalex82]

Hello,

I am debugging messages my device to the coordinator and would like them to be stored in the device state. I added the following converter code:

`
const fromZigbee_LevelCtrl = {
cluster: 'genLevelCtrl',
type: ['commandMoveToLevel', 'commandMoveToLevelWithOnOff', 'commandMove', 'commandMoveWithOnOff',
'commandStop', 'commandStopWithOnOff', 'commandStep', 'commandStepWithOnOff'],

convert: (model, msg, publish, options, meta) => {
    const cmd = msg['type'];
    const payload = msg['data'];

    const result = {level_ctrl: {command: cmd, payload: payload}};
    return result;
},

}
`

The goal here is just to catch all LevelCtrl messages and store them in the device state. This approach basically works, but one thing is working strange.

Imagine it receives a command with payload. The state gets the correct value
"level_ctrl":{"command":"commandMove","payload":{"movemode":1,"rate":80}}

Then it receives a command without payload, and the code above returns
{"level_ctrl":{"command":"commandStop","payload":{}}}

But in the device state the old payload still exists:
MQTT publish: topic 'zigbee2mqtt/my_test_switch' .... "level_ctrl":{"command":"commandStop","payload":{"movemode":1,"rate":80}}...

Is there a way to clear the payload field?