human
Solve the following python programming problem given the following code:
@ gen_test 
def test_aggregate_callback(self) : 
    mongo_2_5_1 = (yield at_least (mongo_2_5_1.cx, (2, 5, 1))) 
    future = Future () 
    def cb(result, error) : 
        if error : 
            future.set_exception (error) 
else : 
            future.set_result (result) 
self.db.test.aggregate (self.pipeline, cursor = False, callback = cb) 
    (yield future) 
    if mongo_2_5_1 : 
        with self.assertRaises (InvalidOperation) : 
            self.db.test.aggregate (self.pipeline, callback = cb) 

    
    

    Fix the buggy line: mongo_2_5_1 = (yield at_least (mongo_2_5_1.cx, (2, 5, 1)))
assistant
#Here is Python code to fix the buggy line: mongo_2_5_1 = (yield at_least (mongo_2_5_1.

mongo_2_5_1 = (yield at_least (self.cx, (2, 5, 1)))