How does ut.Optional work?

I recently learned that ut.Subtractive can be used to exclude specific components in a world.forEach loop.
https://forum.unity.com/threads/filter-components.646471/#post-4344961

I also noticed that there is a ut.Optional function. I tried to use it in the same way like this:

Code (JavaScript):

1. this.world.forEach([game.Component1, game.Component2], [ut.Optional(game.Component3)], (comp1, comp2, comp3) => {
2.     console.log(comp3);
3. });

This seems to work since it does iterate over the right entities, but the comp3 parameter is always undefined. What is the correct way of using this?