Trying to fix PickCharacterActivity.java

Oops.  I just realized that the User class probably isn't yours to change.  In that case it is still a good idea to be explicit about how the routine and your system behave, and then be consistent.  If there are objects that cannot exist unless you have a valid User object, then you can and should assume you have a valid currentUser.  The only place that should validate currentUser or the result from User.getCurrentUser() is when you are in a state where you do not know whether a user exists.  Document the expected behavior, and be consistent.