I just added the read and write methods to my TE and im getting a StackOverflowError in the Chunk IO Worker Thread while writing to the NBT tag. This turned out to be extremely difficult to debug since everything that this thread uses is unmapped and I dont really know how it works. Here is part of the log:  https://pastebin.com/eGd73Uwz. 

This is my write method:

	@Override
	public CompoundNBT write(CompoundNBT compound) {
		super.write(compound);
		compound.put("inventory", ItemStackHelper.saveAllItems(compound, Util.toNonNullList(this.inventory)));

		return compound;
	}
	
//in Util
	public static NonNullList<ItemStack> toNonNullList(IItemHandler inv) {
		NonNullList<ItemStack> out = NonNullList.create();
		for(int i = 0; i < inv.getSlots(); i++)  
			out.add(inv.getStackInSlot(i));
		
		return out;
	}

I have checked the resulting CompoundNBT but it looks just like what I would expect and its not infinitly nested or anything...

I dont really know what to do anymore since any attempts to debug this with breakpoints have led to nothing. If anyone has an idea of whats going on please let me know

yup that did it, thanks