<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_sort_fields(self):
 """ Take care of sorting. """

        sort_fields = ','.join(self.options.sort_fields)
        if sort_fields == '*':
            sort_fields = self.get_output_fields()

        return formatting.validate_sort_fields(sort_fields or config.sort_fields)