human
Solve the following python programming problem given the following code:
def _serialize_hstore(val) : 
    'Serialize a dictionary into an hstore literal.  Keys and values must
    both be strings (except None for values).

    ' 
    def esc(s, position) : 
        if ((position == 'value') and (s is None)) : 
            return 'NULL' 
else : 
            if isinstance (s, util.string_types) : 
                return ('"%s"' % s.replace ('\\', '\\\\').replace ('"', '\\"')) 
else : 
                raise ValueError (('%r in %s position is not a string.' % (s, position))) 
return ', '.join ((('%s=>%s' % (esc (val, 'key'), esc (v, 'value'))) for (k, v) in val.items ())) 

    
    

    Fix the buggy line: return ', '.join ((('%s=>%s' % (esc (val, 'key'), esc (v, 'value'))) for (k, v) in val.items ()))
assistant
#Here is Python program to fix the buggy line: return ', '.

return ', '.join ((('%s=>%s' % (esc (k, 'key'), esc (v, 'value'))) for (k, v) in val.items ()))