Passing null to non-nullable fields

[Lootwig]

Doc of generated call() method says:

All null values passed to non-nullable fields will be ignored.

That's not true, the generated implementation always casts values that are not $CopyWithPlaceholder() (so, also null) to the non-null type for non-nullable fields instead of keeping the old value, leading to an exception.

I'm using version 4.0.0.