human
Solve the following python programming problem given the following code:
def _transform_stats(self, stats) : 
    'Converts stats from pststs.Stats format to call nested dict.' 
    def _statcmp(stat) : 
        'Comparator by cummulative time.' 
        (_, params) = stat 
        return params [3] 
stats.calc_callees () 
    callees = self._build_callees (stats.stats) 
    (root, _) = max (stats.stats.items (), key = _statcmp) 
    return self._build_call_tree (root, callees, _statcmp.stats) 

    
    

    Fix the buggy line: return self._build_call_tree (root, callees, _statcmp.stats)
assistant
#Here is Python program to fix the buggy line: return self.

return self._build_call_tree (root, callees, stats.stats)