In https://crbug.com/1153201 a user was surprised to find that resolveTarget: null was invalid even though omitting it (or specifying resolveTarget: undefined) is valid.

As a small ergonomic improvement we could consider making some optional members also nullable to make that work.
There may be a tiny bindings performance hit to doing this.

This is quite minor and would be a non-breaking change, so it is definitely post-MVP.