Change icon Weather Underground

I try to change the icons in Weather Underground, but i get a question mark instead of the good icon, herse is my script:

  - platform: template
    sensors:
      pws_weather_template:
        friendly_name: 'Weersverwachting'
        value_template: "{{ states('sensor.pws_weather') }}"
        icon_template: >
          {% if is_state('sensor.pws_weather_icon', 'clear') %}
            mdi:weather-sunny
          {% elif is_state('sensor.pws_weather_icon', 'nt_clear') %}
            mdi:weather-night
          {% elif is_state('sensor.pws_weather_icon', 'rain') %}
            mdi:weather-rainy
          {% elif is_state('sensor.pws_weather_icon', 'snow') %}
            mdi:weather-snowy
          {% elif is_state('sensor.pws_weather_icon', 'sleet') %}
            mdi:weather-snowy-rainy
          {% elif is_state('sensor.pws_weather_icon', 'wind') %}
            mdi:weather-windy-variant
          {% elif is_state('sensor.pws_weather_icon', 'fog') %}
            mdi:weather-fog
          {% elif is_state('sensor.pws_weather_icon', 'cloudy') %}
            mdi:weather-cloudy
          {% elif is_state('sensor.pws_weather_icon', 'partlycloudy') or is_state('sensor.pws_weather_icon', 'nt_partlycloudy') %}
            mdi:weather-partlycloudy
          {% elif is_state('sensor.pws_weather_icon', 'hail') %}
            mdi:weather-hail
          {% elif is_state('sensor.pws_weather_icon', 'thunderstorm') %}
            mdi:weather-lightning
          {% else %}
            mdi:help-circle
          {% endif %}

Try test the state with the Icon Description in this doc (case sensitive):

https://docs.google.com/document/d/1qpc4QN3YDpGDGGNYVINh7tfeulcZ4fxPSC5f4KzpR_U/edit

e.g.
{% if is_state(‘sensor.pws_weather’, ‘Clear’) %}
mdi:weather-sunny