Emulated_hue lists some entities with "hue": null

Configuration
1

I have setup the emulated_hue bridge for Alexa with the following configuration:

emulated_hue:
  host_ip: 192.168.178.53
  listen_port: 80
  expose_by_default: true
  exposed_domains:
    - input_boolean
  entities:
    input_boolean.licht_flur_bool:
      name: "Licht Flur"
    input_boolean.waschmaschine_ansage:
      name: "Ansage Waschmaschine"
    input_boolean.gelber_sack_morgen_bool:
      name: "Ansage Gelber Sack"

When I call the URL http://192.168.178.53/api/pi/lights, some of the devices are listed as follows:

"1": {"modelid": "HASS123", "name": "Waschmaschine Fertig", "state": {"bri": 0, "hue": 0, "on": false, "reachable": true, "sat": 0}, "swversion": "123", "type": "Dimmable light", "uniqueid": "input_boolean.waschmaschine_fertig"}

Others are listed so:

"3": {"modelid": "HASS123", "name": "Ansage Waschmaschine", "state": {"bri": 0, "hue": null, "on": true, "reachable": true, "sat": null}, "swversion": "123", "type": "Dimmable light", "uniqueid": "input_boolean.waschmaschine_ansage"},

The point is that if hue is set to null, it is shown as a “normal” switch in the Alexa app, whereas in case hue is 0, the boolean is shown as dimmer.
Why do some input_boolean mapped to hue=null and others to hue=0?