MongoClient with multiple hosts and directConnection=True does not raise an error

>>> client = MongoClient(['localhost:27017', 'localhost:27018'], directConnection=True)

>>> client

MongoClient(host=['localhost:27018', 'localhost:27017'], document_class=dict, tz_aware=False, connect=True, directconnection=True)

>>> client._topology

<Topology <TopologyDescription id: 5ee92ea84355c7f1de7bd6cb, topology_type: Single, servers: [<ServerDescription ('localhost', 27017) server_type: RSPrimary, rtt: 0.000634608000012804>, <ServerDescription ('localhost', 27018) server_type: RSSecondary, rtt: 0.0005638819999944644>]>>