Bluebird Observed - But Is He the New Box Resident?

As posted previously, the first residents of the new bluebird house installed this spring were chickadees. As also posted previously, as soon as the chickadee young left the box, new new residents appeared to move in.
The new residents appear to have completed their construction as the nest made entirely of sticks now reaches the entrance holes.
I finally observed a bird perched several times on the box - turns out the peraching bird was indeed a bluebird. I never saw the bluebird actually enter the box. I have never seen a bluebird nest entirely of sticks. If there are eggs in the nest, I do not see them, but I have not performed a full inspection by pulling the nest out of the box. Has anyone ever seen such a nest of sticks?