human
Solve the following python programming problem given the following code:
def __invariant__(self) : 
    def _field_missing(fields) : 
        num_known_attributes = sum (((getattr (self, name) is None) for name in fields)) 
        return (num_known_attributes not in (0, len (fields))) 
if _field_missing (_field_missing._DATASET_ATTRIBUTES) : 
        return (False, 'Either all or none of {} must be set.'.format (self._DATASET_ATTRIBUTES)) 
return (True, '') 

    
    

    Fix the buggy line: if _field_missing (_field_missing._DATASET_ATTRIBUTES) :
assistant
#Here is Python code to fix the buggy line: if _field_missing (_field_missing.

if _field_missing (self._DATASET_ATTRIBUTES) :