Gui throwing null pointer expression

[knoxi]

Ok, so I've been working on a gui and I've gotten most of it to work but just as I am finishing an error appeared,

Whenever I right click the block instead of showing the gui minecraft crashes.

this is the error message: 

Quote

java.lang.NullPointerException: Ticking entity
    at java.util.Objects.requireNonNull(Objects.java:208) ~[?:?] {}
    at net.minecraft.world.inventory.AbstractContainerMenu.broadcastChanges(AbstractContainerMenu.java:169) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading}
    at net.minecraft.server.level.ServerPlayer.tick(ServerPlayer.java:414) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.level.ServerLevel.tickNonPassenger(ServerLevel.java:657) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.level.Level.guardEntityTick(Level.java:457) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.level.ServerLevel.lambda$tick$3(ServerLevel.java:322) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.world.level.entity.EntityTickList.forEach(EntityTickList.java:53) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading}
    at net.minecraft.server.level.ServerLevel.tick(ServerLevel.java:302) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.tickChildren(MinecraftServer.java:866) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:806) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.client.server.IntegratedServer.tickServer(IntegratedServer.java:84) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:654) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.lambda$spin$2(MinecraftServer.java:245) ~[forge-1.19-41.0.107_mapped_official_1.19-recomp.jar%23181!/:?] {re:classloading,pl:accesstransformer:B}
    at java.lang.Thread.run(Thread.java:833) ~[?:?] {}
 

and this is my code:

ExampleChestScreen.java:

public class ExampleChestScreen extends AbstractContainerScreen<ExampleChestContainer> {
    private static final ResourceLocation TEXTURE = new ResourceLocation(KnoxiItems.MOD_ID,
            "textures/gui/magical_workbench_gui.png");

    private ExtendedButton beanButton;

    public ExampleChestScreen(ExampleChestContainer container, Inventory playerInv, Component title) {
        super(container, playerInv, title);
        this.leftPos = 0;
        this.topPos = 0;
    }

    @Override
    public void render(PoseStack stack, int mouseX, int mouseY, float partialTicks) {
        super.render(stack, mouseX, mouseY, partialTicks);
        this.font.draw(stack, this.title, this.leftPos + 20, this.topPos + 5, 0x404040);
        this.font.draw(stack, this.playerInventoryTitle, this.leftPos + 8, this.topPos + 75, 0x404040);
    }

    @Override
    protected void init() {
        super.init();
        this.beanButton = addRenderableWidget(
                new ExtendedButton(this.leftPos, this.topPos, 16, 16, Component.literal("beans"),
                        btn -> Minecraft.getInstance().player.displayClientMessage(Component.literal("beans"), false)));
    }

    @Override
    protected void renderBg(PoseStack stack, float mouseX, int mouseY, int partialTicks) {
        renderBackground(stack);
        RenderSystem.setShader(GameRenderer::getPositionTexShader);
        RenderSystem.setShaderColor(1.0f, 1.0f, 1.0f, 1.0f);
        RenderSystem.setShaderTexture(0, TEXTURE);
        blit(stack, this.leftPos, this.topPos, 0, 0, this.imageWidth, this.imageHeight);
    }

    @Override
    protected void renderLabels(PoseStack stack, int mouseX, int mouseY) {
    }
}

ExampleChestBlockEntity.java:

public class ExampleChestBlockEntity extends BlockEntity {
    public static Component TITLE = Component.literal("Example Chest");
    IItemHandler inventory;
    public ExampleChestBlockEntity(BlockPos pos, BlockState state) {
        super(ModBlockEntities.EXAMPLE_CHEST.get(), pos, state);
        inventory = new IItemHandler() {
            private ItemStack[] Inventory = new ItemStack[27];
            @Override
            public int getSlots() {
                return Inventory.length;
            }

            @Override
            public @NotNull ItemStack getStackInSlot(int slot) {
                return Inventory[slot];
            }

            @Override
            public @NotNull ItemStack insertItem(int slot, @NotNull ItemStack stack, boolean simulate) {
                Inventory[slot] = stack;
                return Inventory[slot];
            }

            @Override
            public @NotNull ItemStack extractItem(int slot, int amount, boolean simulate) {
                if (!(amount >= Inventory[slot].getCount())) {
                    Inventory[slot] = new ItemStack(Inventory[slot].getItem(), Inventory[slot].getCount() - amount);
                } else {
                    Inventory[slot] = null;
                }
                return Inventory[slot];
            }

            @Override
            public int getSlotLimit(int slot) {
                return 64;
            }

            @Override
            public boolean isItemValid(int slot, @NotNull ItemStack stack) {
                return true;
            }
        };
    }
}

ExampleChestContainer.java:

public class ExampleChestContainer extends AbstractContainerMenu {
    private final ContainerLevelAccess containerAccess;

    // Client Constructor
    public ExampleChestContainer(int id, Inventory playerInv) {
        this(id, playerInv, new ItemStackHandler(27), BlockPos.ZERO);
    }

    // Server constructor
    public ExampleChestContainer(int id, Inventory playerInv, IItemHandler slots, BlockPos pos) {
        super(ModBlockContainers.EXAMPLE_CHEST.get(), id);
        this.containerAccess = ContainerLevelAccess.create(playerInv.player.level, pos);

        final int slotSizePlus2 = 18, startX = 8, startY = 86, hotbarY = 144, inventoryY = 18;

        for (int row = 0; row < 3; row++) {
            for (int column = 0; column < 9; column++) {
                addSlot(new SlotItemHandler(slots, row * 9 + column, startX + column * slotSizePlus2,
                        inventoryY + row * slotSizePlus2));
            }
        }

        for (int row = 0; row < 3; row++) {
            for (int column = 0; column < 9; column++) {
                addSlot(new Slot(playerInv, 9 + row * 9 + column, startX + column * slotSizePlus2,
                        startY + row * slotSizePlus2));
            }
        }

        for (int column = 0; column < 9; column++) {
            addSlot(new Slot(playerInv, column, startX + column * slotSizePlus2, hotbarY));
        }
    }

    @Override
    public ItemStack quickMoveStack(Player player, int index) {
        var retStack = ItemStack.EMPTY;
        final Slot slot = getSlot(index);
        if (slot.hasItem()) {
            final ItemStack item = slot.getItem();
            retStack = item.copy();
            if (index < 27) {
                if (!moveItemStackTo(item, 27, this.slots.size(), true))
                    return ItemStack.EMPTY;
            } else if (!moveItemStackTo(item, 0, 27, false))
                return ItemStack.EMPTY;

            if (item.isEmpty()) {
                slot.set(ItemStack.EMPTY);
            } else {
                slot.setChanged();
            }
        }

        return retStack;
    }

    @Override
    public boolean stillValid(Player player) {
        return stillValid(this.containerAccess, player, ModBlocks.EXAMPLE_CHEST.get());
    }

    public static MenuConstructor getServerContainer(ExampleChestBlockEntity chest, BlockPos pos) {
        return (id, playerInv, player) -> new ExampleChestContainer(id, playerInv, chest.inventory, pos);
    }
}

ExampleChestBlock.java:

public class ExampleChestBlock extends HorizontalDirectionalBlock implements EntityBlock {
    public ExampleChestBlock(Properties properties) {
        super(properties);
        registerDefaultState(defaultBlockState().setValue(FACING, Direction.NORTH));
    }

    @Override
    public BlockState getStateForPlacement(BlockPlaceContext context) {
        return defaultBlockState().setValue(FACING, context.getHorizontalDirection().getOpposite());
    }

   /* @Override
    public <T extends BlockEntity> BlockEntityTicker<T> getTicker(Level level, BlockState state,
                                                                  BlockEntityType<T> beType) {
        //return level.isClientSide ? null
        //        : (level0, pos, state0, blockEntity) -> ((ExampleChestBlockEntity) blockEntity).tick();
        return super.defaultBlockState().getTicker(level, beType);
    }*/

    @Nullable
    @Override
    public <T extends BlockEntity> BlockEntityTicker<T> getTicker(Level p_153212_, BlockState p_153213_, BlockEntityType<T> p_153214_) {
        return EntityBlock.super.getTicker(p_153212_, p_153213_, p_153214_);
    }

    @Override
    public BlockEntity newBlockEntity(BlockPos pos, BlockState state) {
        return new ExampleChestBlockEntity(pos, state);
    }

    @Override
    public InteractionResult use(BlockState state, Level level, BlockPos pos, Player player, InteractionHand hand,
                                 BlockHitResult result) {
        if (!level.isClientSide && level.getBlockEntity(pos) instanceof final ExampleChestBlockEntity chest) {
            final MenuProvider container = new SimpleMenuProvider(ExampleChestContainer.getServerContainer(chest, pos),
                    ExampleChestBlockEntity.TITLE);
            NetworkHooks.openScreen((ServerPlayer) player, container, pos);
        }

        return InteractionResult.SUCCESS;
    }

    @Override
    protected void createBlockStateDefinition(StateDefinition.Builder<Block, BlockState> builder) {
        super.createBlockStateDefinition(builder);
        builder.add(FACING);
    }
}

Thank you in advance for any help

[warjort]

Look at the code where it crashes. It has an itemStack::copy of the item stack in each slot.

The error says one of your slots contains a null, when you should be using ItemStack.EMPTY for unoccupied slots.

[warjort]

The vanilla chest uses 

Quote

   private NonNullList<ItemStack> items = NonNullList.withSize(27, ItemStack.EMPTY);
 

For its items.

[knoxi]

Thanks but now it says this when i right click it:

Quote

[07:34:18] [Render thread/WARN] [minecraft/MenuScreens]: Failed to create screen for menu type: knoxiitems:example_chest

 

[Luis_ST]

You need to register a Screen for your Menu in FMLClientSetupEvent in #enqueueWork via MenuScreens#register.
If you already register a Screen for your Menu, please post the code you are using for it.