While we might never be able to have 100% of our code strict, we can at
the very least do it for all of our tests. This ensures that our tests
are using our API with the types as intended by the test author, and not
silently be cast to what our API requires.
Fix#2810. Repairing some Phpstan diagnostics, used `?:` rather than `??` in a few places.
2 different Html modules are affected. Also, Ods Reader, but its problem is with sheet title rather than cell contents. And, as it turns out, Ods Reader was already not handling sheets with a title of `0` correctly - it made a truthy test before setting sheet title. That is now changed to truthy or numeric. Other readers are not susceptible to this problem. Tests are added.
Adrien Crivelli
oleibman