def _GetAdditionalProperty(properties, property_key, not_found_value='Unknown'):
  """Gets the value for the given key in a list of properties.

  Looks through a list of properties and tries to find the value for the given
  key. If it's not found, not_found_value is returned.

  Args:
    properties: A dictionary of key string, value string pairs.
    property_key: The key string for which we want to get the value.
    not_found_value: The string value to return if the key is not found.

  Returns:
    A string containing the value for the given key, or `not_found_value` if
    the key is not found.
  """
  for prop in properties:
    if prop.key == property_key:
      if hasattr(prop, 'value'):
        return prop.value
      break
  return not_found_value