code: def set_prop_if_null(name, props, if_null):
      # type: (str, Dict[str, Any], Any) -> None
      
      value = get_prop_value(name, props)
      if value is None:
          props[name] = if_null
docs: Updates the value of a property if the previous one was None
  
      :param name: Name of the property
      :param props: Dictionary of properties
      :param if_null: Value to insert if the previous was None