InvalidPluginException: java.lang.NullPointerException

Question

Thanks for your help! The plugin finally works. Indeed, p was null, so I changed that and it worked

Answer 1

When you initialise MenuInv you get a NullPointerException.

See these 2 lines:

Player p;
PlayerInventory pi = p.getInventory();

The 2nd one throws the NullPointerExxception because p is null.