`TraversedJSONPathBuilder` and `undefined` results

[sbossarte]

When using the TraversedJSONPathBuilder, I often find myself needing to strip undefined from the resulting type, which $notNull is not sufficient for, and $castTo ends up being verbose. For example:

db.selectFrom('elements')
	.select(eb => [
		'id',
		eb.ref('data', '->$')
			.key('flags')
			.$castTo<Exclude<ElementData['flags'], undefined>>()
			.as('flags'),
	])
	.where(eb => eb(eb.ref('data', '->$').key('flags'), 'is not', null))

With this, I was wondering if perhaps the type returned by TraversedJSONPathBuilder should use null instead of undefined since the database doesn't actually returned undefined in these cases, does it? Or if it does, then a $notUndefined may be more appropriate?