code: def GetAttribute(self, identifier):
      
      if not self._is_parsed:
        self._Parse()
        self._is_parsed = True
  
      if identifier not in self._attributes:
        return None
  
      return self._attributes[identifier]
docs: Retrieves a specific attribute.
  
      Args:
        identifier (str): identifier of the attribute within the volume.
  
      Returns:
        VolumeAttribute: volume attribute or None if not available.