Question around Authentication API

[OUCHUNYU]

Thanks for building this great platform.
I just started to play around with the wsandroid code base. The first thing I noticed was that for every authentication, the Android app makes a post request to this API endpoint /services/rest/user/logout, to log out first before calling /services/rest/user/login to login. The response for /services/rest/user/logout is 406.
I wonder what is the reason for calling log out before logging in? If it is still necessary.