Get qualifiers. Correct for inconsistent capitalization in GAF files

def _get_qualifier(val):
        """Get qualifiers. Correct for inconsistent capitalization in GAF files"""
        quals = set()
        if val == '':
            return quals
        for val in val.split('|'):
            val = val.lower()
            quals.add(val if val != 'not' else 'NOT')
        return quals