def METHOD_NAME(self):
    if len(self.fill_value) == 0:
        return
    if len(self.fill_value) == 1:
        fill_value = str(self.fill_value[0])
        new_features = [fill_value] * len(self.append_header)
        append_value = DELIMITER.join(new_features)
    else:
        append_value = DELIMITER.join([str(v) for v in self.fill_value])
    return append_value