Almost certain to be at least a small block. It's needed to help keep the two sides glued together at the back, otherwise there would only be a butt joint keeping them in place.

Too late now, but it's really not a good idea to use anything other than a non-waterproof woodworking glue for neck joints. If you ever need to take the neck off because you find it's at the wrong angle, then with the wrong glue, you can't.