Template sensor: how to prevent 'unknown' with {{is_state('switch.source', 'on') }}

HI i have several template sensors that error out on startup because the sensors they read are not yet updated.

on https://home-assistant.io/components/sensor.template/#considerations it is stated you can prevent that using {{is_state(‘switch.source’, ‘on’) }}, where both used sensors have ever changing states…?

How would i do that in this case:

- platform: template
      value_template: "{{ (13.12 + 0.6215*float(states.sensor.br_temperature.state) + 
                        0.3965*(float(states.sensor.br_temperature.state) - 28.676) *
                  (float(states.sensor.br_wind_speed.state)*3.6)**0.16) | round(2) }}"
      unit_of_measurement: "°C"
      friendly_name: Jag/Ti Wchill

same goes for:

- platform: mold_indicator
  name: Schimmel sensor
  indoor_temp_sensor: sensor.temperatuur_living
  indoor_humidity_sensor: sensor.luchtvochtigheid_living
  outdoor_temp_sensor: sensor.br_temperature
  calibration_factor: 1.16

Please have a look,

I’m having the same problem resulting in some ugly charts. Even when using entity_id and state_attr. There needs to be better startup logic.