<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_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