<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _get_contigs_to_keep(self, filename):
        '''Returns a set of names from file called filename. If filename is None, returns an empty set'''
        if filename is None:
            return set()

        with open(filename) as f:
            return {line.rstrip() for line in f}