Code

@SubscribeEvent
    public void itemPickedUp(EntityItemPickupEvent event){
        System.out.println("Event Works!");
        if(event.entity instanceof EntityPlayer){
            EntityPlayer player = event.entityPlayer;
            EntityItem item = event.item;
            MinefusInventoryPlayer invMinefus = ExtendedPlayer.get(player).inventory;
            if(player.inventory.getFirstEmptyStack() == -1){
                System.out.println("first Slot empty player inv:" + player.inventory.getFirstEmptyStack());
                if(invMinefus.getFirstEmptyStack() == -1){
                    System.out.println("first Slot empty minefus inv:" + invMinefus.getFirstEmptyStack());
                }else{
                    System.out.println("first Slot empty minefus inv:" + invMinefus.getFirstEmptyStack());
                    int slotId = invMinefus.getFirstEmptyStack();
                    if(invMinefus.isItemValidForSlot(slotId, event.item.getEntityItem()) == true){

                        System.out.println("item name" + event.item.getEntityItem().getDisplayName());

                        ItemStack itemStack = event.item.getEntityItem();
                        invMinefus.setInventorySlotContents(slotId, itemStack);
                        event.setCanceled(true);
                    }
                }
            }
        }
    }