Im attempting to use NBT Tags to save an array of block locations, matching with player names. I am trying to save this to my item. But it isn't working. I crash with this:  
 
	public ItemStack onItemRightClick(ItemStack itemstack , World world, EntityPlayer player){
	itemstack = player.getCurrentEquippedItem();
	NBTTagCompound nbt = itemstack.getTagCompound();
	if(!world.isRemote)
	{
		if(player.isSneaking()){
			String i = nbt.getString("HELLO!");
			player.sendChatToPlayer(i);
		}else{
		nbt.setString("name", "YOLO");
		}
	}
	return itemstack;
}
 
(Also this is my first mod and also just a test to see if it will work). If there is a better way to save block location and player names. Please say! Also I need it to still contain this info even after restart. I am trying to make a protection mod and have everything working besides this! Please help if you can