Gui Crashes Minecraft

[Schleim_time]

i looked around the internet to create an GUI and i tried my best to create an gui that shouldnt be able to do anything right now, i only wanted to test out if it will work but my minecraft crashed all the time and i dont know the mistakeforgebench.javaforgebenchcontainer.javaforgebenchgui.javaforgebenchinventory.java

thats my code and here the crash log, it seems all caused by one null pointer but why and how?

 

[17:43:48] [Server thread/FATAL] [minecraft/MinecraftServer]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException: The validated object is null
    at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_211]
    at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_211]
    at net.minecraft.util.Util.runTask(Util.java:54) [Util.class:?]
    at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:798) [MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:743) [MinecraftServer.class:?]
    at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:192) [IntegratedServer.class:?]
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:592) [MinecraftServer.class:?]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_211]
Caused by: java.lang.NullPointerException: The validated object is null
    at org.apache.commons.lang3.Validate.notNull(Validate.java:225) ~[commons-lang3-3.5.jar:3.5]
    at org.apache.commons.lang3.Validate.notNull(Validate.java:206) ~[commons-lang3-3.5.jar:3.5]
    at net.minecraft.util.NonNullList.add(NonNullList.java:62) ~[NonNullList.class:?]
    at java.util.AbstractList.add(Unknown Source) ~[?:1.8.0_211]
    at net.minecraft.inventory.Container.getInventory(Container.java:75) ~[Container.class:?]
    at net.minecraft.inventory.Container.addListener(Container.java:61) ~[Container.class:?]
    at net.minecraftforge.fml.common.network.internal.FMLNetworkHandler.openGui(FMLNetworkHandler.java:101) ~[FMLNetworkHandler.class:?]
    at net.minecraft.entity.player.EntityPlayer.openGui(EntityPlayer.java:2809) ~[EntityPlayer.class:?]
    at com.Schleimtime.Wasteland.blocks.castfurnace.forgebench.onBlockActivated(forgebench.java:56) ~[forgebench.class:?]
    at net.minecraft.server.management.PlayerInteractionManager.processRightClickBlock(PlayerInteractionManager.java:475) ~[PlayerInteractionManager.class:?]
    at net.minecraft.network.NetHandlerPlayServer.processTryUseItemOnBlock(NetHandlerPlayServer.java:769) ~[NetHandlerPlayServer.class:?]
    at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.processPacket(CPacketPlayerTryUseItemOnBlock.java:68) ~[CPacketPlayerTryUseItemOnBlock.class:?]
    at net.minecraft.network.play.client.CPacketPlayerTryUseItemOnBlock.processPacket(CPacketPlayerTryUseItemOnBlock.java:13) ~[CPacketPlayerTryUseItemOnBlock.class:?]
    at net.minecraft.network.PacketThreadUtil$1.run(PacketThreadUtil.java:21) ~[PacketThreadUtil$1.class:?]
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_211]
    at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_211]
    at net.minecraft.util.Util.runTask(Util.java:53) ~[Util.class:?]
    ... 5 more
[17:43:48] [Server thread/ERROR] [minecraft/MinecraftServer]: Encountered an unexpected exception
net.minecraft.util.ReportedException: Ticking player
    at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:848) ~[MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:743) ~[MinecraftServer.class:?]
    at net.minecraft.server.integrated.IntegratedServer.tick(IntegratedServer.java:192) ~[IntegratedServer.class:?]
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:592) [MinecraftServer.class:?]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_211]
Caused by: java.lang.NullPointerException
    at net.minecraft.item.ItemStack.areItemStacksEqual(ItemStack.java:495) ~[ItemStack.class:?]
    at net.minecraft.inventory.Container.detectAndSendChanges(Container.java:100) ~[Container.class:?]
    at net.minecraft.entity.player.EntityPlayerMP.onUpdate(EntityPlayerMP.java:365) ~[EntityPlayerMP.class:?]
    at net.minecraft.world.World.updateEntityWithOptionalForce(World.java:2171) ~[World.class:?]
    at net.minecraft.world.WorldServer.updateEntityWithOptionalForce(WorldServer.java:871) ~[WorldServer.class:?]
    at net.minecraft.world.World.updateEntity(World.java:2130) ~[World.class:?]
    at net.minecraft.world.WorldServer.tickPlayers(WorldServer.java:672) ~[WorldServer.class:?]
    at net.minecraft.world.World.updateEntities(World.java:1906) ~[World.class:?]
    at net.minecraft.world.WorldServer.updateEntities(WorldServer.java:643) ~[WorldServer.class:?]
    at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:842) ~[MinecraftServer.class:?]
    ... 4 more

[Schleim_time]

public class guihandler implements IGuiHandler{

    @Override
    public Object getServerGuiElement(int ID, EntityPlayer player, World world, int x, int y, int z) {
        if(ID == reference.GUI_FORGEBENCH) {
        forgebenchcontainer con = new forgebenchcontainer(player.inventory, new forgebenchinventory());
        return con;
        } else {return null;}
    }

    @Override
    public Object getClientGuiElement(int ID, EntityPlayer player, World world, int x, int y, int z) {
        if(ID == reference.GUI_FORGEBENCH) {
            forgebenchgui gui = new forgebenchgui(player.inventory, new forgebenchinventory());
            return gui;
        } else {return null;}
    }

}

 

and thats my handler

[Schleim_time]

 ok okay i did something completly whrong at end, but the game still crashes for the same reason, now i extended with a tileentity and registered it and addet to the block and all that stuff