When a client instance logs in / registers, the response contains, among other things, a home_server field. Currently, this information is stored as a .hs member of the instance. However, if the MatrixClient is created with an exiting token, no such registration/login takes plave, hence no response is received, and the instance doesn't set this member -- which means that code can't rely on its being there.
At the moment, this information isn't used anywhere in the code, so probably the best thing to do is to just remove it.