Major Description
MockResolver.getMountPoints() breaks the semantic of FileSubclusterResolver.getMountPoints(). Currently it returns null when the path is a mount point and no mount points are under the path.
Return zero-length list if the path is a mount point but there are no mount points under the path.
This is required by router federation rename. I found this bug when writing unit test for the rbf rename. Let's fix it here to avoid mixing up with the router federation rename.