PR
#4801 fixes numerous bugs that arose from recent PRs. It replaces tests against None with so-called "truthy" tests.
I welcome any comments and suggestions about PR #4801. I merged this PR
"early" because imo it's impossible to evaluate the PR just by reading
the diffs.
I've
put a lot of work into this PR, but further work may be required.
Please keep testing Leo's "devel" branch and report any problems.
Edward