2sxc 08.01.02

Mostly non-critical bugfixes see https://github.com/2sic/2sxc/issues?q=is%3Aissue+milestone%3A%222sxc+v8.01.02+Quickfixes%22+is%3Aclosed

Note that I made some changes to how null-values are serialized. To 99% no side-effects, but there is a 1% chance that it could affect import/export