Function
The lesson as the catalog holds it
The lesson's absolute URL
A schema.org VideoObject, or null when the lesson is undated
Returns null when the lesson declares no uploadDate. Google requires one
on VideoObject, so emitting the type without it produces structured data
validators reject — worse than emitting none, because invalid markup can
suppress the rest of a page's results. Most of the catalog is undated today,
which is why the absent case is the common one rather than the edge.
A Lecture's video — or nothing.