Custom Attribute Modifiers

Hello,

I've recently been trying to create custom attributes for items and I have seen a few threads demonstrating this but when I tried this for myself, it ended up with an error.

Error:

Code:

 // Get NMS version
                    net.minecraft.server.v1_16_R3.ItemStack itemStack = CraftItemStack.asNMSCopy(item);

                    // Get NBT Tags
                    NBTTagCompound nbt = itemStack.hasTag() ? itemStack.getTag() : new NBTTagCompound();

                    // Get all AttributeModifiers in a list
                    NBTTagList modifiers = nbt.getList("AttributeModifiers", 10);

                    // Creating new attribute
                    NBTTagCompound attribute = new NBTTagCompound();
                    attribute.setString("AttributeName", "Test");
                    attribute.setString("Name", "attribute.name.Test");
                    attribute.setInt("Amount", 25);
                    attribute.setInt("Operation", 0);
                    attribute.setInt("UUIDLeast", 894654);
                    attribute.setInt("UUIDMost",2872);
                    attribute.setString("Slot","mainhand");

                    // Add the new attribute to the list of current ones
                    modifiers.add(attribute);

                    // Set the nbt's old modifiers to the new list
                    nbt.set("AttributeModifiers", modifiers);

                    // Set the old NBT to the new NBT
                    itemStack.setTag(nbt);

                    // Assign the variable the new item
                    item = CraftItemStack.asBukkitCopy(itemStack);

 

@Rexe0 please direct us to the line in the code that is causing the error

 

It does not print a full stack trace when giving myself the item, nor does it give me the line at which the error is taking place. It only gives me the: 'Unable to create attribute: null.'