Storing Objects in ItemStack Capability Storage

[Dexter12]

I am trying to store data through my ItemStack capability storage, but I stumbled upon a roadblock.

My ItemStack Capability Storage:

public class WandItemStorage implements Capability.IStorage<IWandCap>
{
    @Nullable
    @Override
    public INBT writeNBT(Capability<IWandCap> capability, IWandCap instance, Direction side)
    {
        CompoundNBT tag = new CompoundNBT();
        tag.put("spells", instance.getSpells());
        return tag;
    }

    @Override
    public void readNBT(Capability<IWandCap> capability, IWandCap instance, Direction side, INBT nbt)
    {
        
    }
}

My ItemStack Capability:

public class WandCap implements IWandCap
{
    private List<Spell> spells;

    public WandCap ()
    {
        spells = new ArrayList<>();
    }

    @Override
    public List<Spell> getSpells()
    {
        return this.spells;
    }

    @Override
    public void addSpells(Spell... spells)
    {
        this.spells.addAll(Arrays.asList(spells));
    }

    @Override
    public void addSpell(Spell spell)
    {
        this.spells.add(spell);
    }

    @Override
    public void removeSpells(Spell... spells)
    {
       this.spells.removeAll(Arrays.asList(spells));
    }

    @Override
    public void removeSpell(Spell spell)
    {
        this.spells.remove(spell);
    }

    @Override
    public boolean containsSpell(Spell spell)
    {
        return this.spells.contains(spell);
    }
}

I'm currently trying to put a List of Spells (my custom object) to the Write and Read NBT methods of my ItemStack cap storage, but CompoundNBT doesn't have a method for putting a custom object into a tag. All it has is the put() method from what I'm seeing, however the put() method requires an INBT for the second parameter, which I do not have. Would I need to convert my List of Spells to an INBT, and how would I go about doing that?

[diesieben07]

For registry-based things (like blocks for example) just store their registry name (e.g. "minecraft:stone").

For maps, lists and other collections you usually want to use ListNBT.

For custom complex objects you need to break them down into their primitive parts. For example if you have a class with a String field and a double field, you'd store that class into a CompoundNBT with one string value and one double value.