Hide header icon in custom:simple-thermostat

must be missing the obvious, but how can we not show a default icon in the card header?

type: custom:simple-thermostat
entity: climate.front_room
name: Front room
decimals: 1
sensors:

is what I use now, but if I try

type: custom:simple-thermostat
entity: climate.front_room
header:
  name: Front room
  icon: none/null/''
decimals: 1
sensors:

it always defaults to the radiator…

cant this be done? I didnt find anything in GitHub - nervetattoo/simple-thermostat: A different take on the thermostat card for Home Assistant ♨️ nor any other section in the docs. or?

please have a look? thanks!