'Returns a message if an hda is not ready to be used in visualization.'

def data_conversion_status(self, hda):

    if (not hda):
        return self.model_class.conversion_messages.NO_DATA
    if (hda.state == model.Job.states.ERROR):
        return self.model_class.conversion_messages.ERROR
    if (hda.state != model.Job.states.OK):
        return self.model_class.conversion_messages.PENDING
    return None
