can press s to go to store (bugged still)

i had a hard time as at first the jump upgrade was reporting errors and
after i fixed that, when pressing the back button to leave the store it
was reporting
java.lang.NullPointerException: The given world cannot be null.
at Back.act(Back.java:47)

sorry that it isn't completely ready, i just don't have any idea of how
to fix that