Capabalities ошибка

[Goremore]

Привет пытаюсь сделать своё capabalities. Когда пытаюсь прикрепить к игроку вылазит ошибка.
Вот все классы:

package com.example.examplemod.capabilities;

public interface IMana {

    public void setMana(int mana);

    public int getMana();
}

package com.example.examplemod.capabilities;

public class Mana implements IMana{

    private int mana = 1;

    @Override
    public void setMana(int mana) {
        this.mana = mana;
    }

    @Override
    public int getMana() {
        return this.mana;
    }
}

package com.example.examplemod.capabilities;

import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.EnumFacing;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.CapabilityInject;
import net.minecraftforge.common.capabilities.ICapabilitySerializable;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

public class ManaProvider implements ICapabilitySerializable<NBTTagCompound> {


    @CapabilityInject(IMana.class)
    public static final Capability<IMana> MANA_CAPABILITY = null;
    private final IMana capability = new Mana();

    @Override
    public boolean hasCapability(@Nonnull Capability<?> capability, @Nullable EnumFacing facing) {
        return capability == MANA_CAPABILITY;
    }

    @Nullable
    @Override
    @SuppressWarnings("unchecked")
    public <T> T getCapability(@Nonnull Capability<T> capability, @Nullable EnumFacing facing) {
        if ((MANA_CAPABILITY != null) && (capability == MANA_CAPABILITY)) return (T) this.capability;
        return null;
    }

    @Override
    public NBTTagCompound serializeNBT() {
        return (NBTTagCompound) ManaStorage.INSTANCE.writeNBT(ManaProvider.MANA_CAPABILITY, new Mana(), null);
    }

    @Override
    public void deserializeNBT(NBTTagCompound nbt) {
        ManaStorage.INSTANCE.readNBT(ManaProvider.MANA_CAPABILITY, new Mana(), null, nbt);
    }
}

package com.example.examplemod.capabilities;

import net.minecraft.nbt.NBTBase;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.EnumFacing;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.Capability.IStorage;

import javax.annotation.Nullable;

public class ManaStorage implements IStorage<IMana> {

    public static final ManaStorage INSTANCE = new ManaStorage();

    @Nullable
    @Override
    public NBTBase writeNBT(Capability<IMana> capability, IMana instance, EnumFacing side) {
        NBTTagCompound nbt = new NBTTagCompound();
        nbt.setInteger("maxMana",instance.getMana());
        return null;
    }

    @Override
    public void readNBT(Capability<IMana> capability, IMana instance, EnumFacing side, NBTBase nbt) {
        NBTTagCompound tag = (NBTTagCompound) nbt;
        instance.setMana(tag.getInteger("maxMana"));
    }
}

package com.example.examplemod.util.handlers;

import com.example.examplemod.capabilities.ManaProvider;
import com.example.examplemod.util.Reference;
import net.minecraft.entity.Entity;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.util.ResourceLocation;
import net.minecraftforge.event.AttachCapabilitiesEvent;

import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;

import java.util.Locale;


@Mod.EventBusSubscriber
public class Handler {


    @SubscribeEvent
    public static void attachEntity(AttachCapabilitiesEvent<Entity> event) {
        if (event.getObject() instanceof EntityPlayer) {
            ManaProvider manaCap = new ManaProvider();

            event.addCapability(new ResourceLocation(Reference.MODID, "mana_capability"), manaCap);

        }
    }

}

Быстрее всего напутал что-то с nbt. Помогите пожалуйста.

 

[Goremore]

Нашёл ошибка забывал возвращать nbt в методе writeNBT.

package com.example.examplemod.capabilities;

import net.minecraft.nbt.NBTBase;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.EnumFacing;
import net.minecraftforge.common.capabilities.Capability;
import net.minecraftforge.common.capabilities.Capability.IStorage;

public class ManaStorage implements IStorage<IMana> {

    public static final ManaStorage INSTANCE = new ManaStorage();


    @Override
    public NBTBase writeNBT(Capability<IMana> capability, IMana instance, EnumFacing side) {
        NBTTagCompound nbt = new NBTTagCompound();
        nbt.setInteger("Mana",instance.getMana());
        return nbt;
    }

    @Override
    public void readNBT(Capability<IMana> capability, IMana instance, EnumFacing side, NBTBase nbt) {
        NBTTagCompound tag = (NBTTagCompound) nbt;
        instance.setMana(tag.getInteger("Mana"));
    }
}