DM-9873 added support for None to be added to PropertyList. Update afw FITS reading to support undefined values.
PropertySet does not support values of None
price thanks for agreeing to review. The changes are at https://github.com/lsst/afw/pull/446/files and depend on DM-9873 changes to daf_base.
The substantive changes are small, with the bulk of the PR being test changes.