The lesson to link to, or null when the first course has no lesson
Remarks
A reference course is never the first course, whatever its sequence. A
reading lesson has no runtime, and the home then names the course alone
rather than claiming a length.
It lives beside the page because it is that page's projection of the
catalog, not a general-purpose utility.
The lesson the new-visitor home's primary action opens: the first lesson of the first level course, with its runtime in whole minutes.