Test failure - MockupDB aggregate tests fails

 [2019/06/12 16:46:01.907] ERROR: test_aggregate_with_mode_primary (tests.test_op_msg_read_preference.TestOpMsgReplicaSet)

 [2019/06/12 16:46:01.907] ----------------------------------------------------------------------

 [2019/06/12 16:46:01.907] Traceback (most recent call last):

 [2019/06/12 16:46:01.907]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/pymongo-mockup-tests/tests/test_op_msg_read_preference.py", line 169, in test

 [2019/06/12 16:46:01.907]     request.reply(operation.reply)

 [2019/06/12 16:46:01.907]   File "/opt/python/2.7/lib/python2.7/contextlib.py", line 24, in __exit__

 [2019/06/12 16:46:01.907]     self.gen.next()

 [2019/06/12 16:46:01.907]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/pymongo-mockup-tests/.eggs/mockupdb-1.8.0.dev0-py2.7.egg/mockupdb/__init__.py", line 197, in going

 [2019/06/12 16:46:01.907]     future(timeout=10)

 [2019/06/12 16:46:01.907]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/pymongo-mockup-tests/.eggs/mockupdb-1.8.0.dev0-py2.7.egg/mockupdb/__init__.py", line 150, in get_result

 [2019/06/12 16:46:01.908]     reraise(*error)

 [2019/06/12 16:46:01.908]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/pymongo-mockup-tests/.eggs/mockupdb-1.8.0.dev0-py2.7.egg/mockupdb/__init__.py", line 135, in target

 [2019/06/12 16:46:01.908]     result[0] = fn(*args, **kwargs)

 [2019/06/12 16:46:01.908]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/pymongo-mockup-tests/tests/operations.py", line 75, in <lambda>

 [2019/06/12 16:46:01.908]     lambda client: client.db.collection.aggregate([]),

 [2019/06/12 16:46:01.908]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/mockuptests/lib/python2.7/site-packages/pymongo/collection.py", line 2372, in aggregate

 [2019/06/12 16:46:01.908]     **kwargs)

 [2019/06/12 16:46:01.908]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/mockuptests/lib/python2.7/site-packages/pymongo/collection.py", line 2292, in _aggregate

 [2019/06/12 16:46:01.908]     retryable=not dollar_out)

 [2019/06/12 16:46:01.908]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/mockuptests/lib/python2.7/site-packages/pymongo/mongo_client.py", line 1457, in _retryable_read

 [2019/06/12 16:46:01.908]     return func(session, server, sock_info, slave_ok)

 [2019/06/12 16:46:01.908]   File "/data/mci/762694d4e15194d43c7b55100aae21a2/mockuptests/lib/python2.7/site-packages/pymongo/aggregation.py", line 145, in get_cursor

 [2019/06/12 16:46:01.908]     ns = cursor["ns"]

 [2019/06/12 16:46:01.908] KeyError: "'ns'"