Improve types in Folio getUserWithCql/escapeCql

[berndoberknapp]

Depending on the PHP version and configuration str_replace might throw a TypeError when the third parameter is null. This can happen in the Folio driver for the password, for example when Shibboleth authentication is used. This PR fixes the issue by adding an empty string as default value when the password is null.

[demiankatz]

Thanks, @berndoberknapp, this looks great, but I would suggest breaking the solution into two parts:

Part 1: let's add the null coalescing to blank string when escaping the password in a separate PR against the release-11.0 branch -- this way, we can get the fundamental part of the fix into the next minor release without changing any method signatures.

Part 2: after that is done, we can merge the rest of this into the dev-12.0 branch, so the BC-breaking signature changes can go into the next major release.

I think that gets us an immediate functional fix while putting the signature changes into the least disruptive place.

If you don't have time to open the separate release-11.0 PR, I'm happy to do that work -- but I wanted to make sure you are okay with this strategy before I implement it.

[demiankatz]

For now I'm re-targeting this PR against dev-12.0 so we don't lose track of it or merge it prematurely, but I'll hold off on approving/merging until we've done the backporting of the null coalescing.

[berndoberknapp]

I can create a separate PR with just the null coalescing for release-11.0 and remove that part from this PR.

[demiankatz]

Thanks, @berndoberknapp. Don't worry about making changes to this PR -- if you just open the separate one against release-11.0, I can merge it through to this one, which should resolve without conflicts and leave the other changes to be merged separately.

[demiankatz]

Thanks for #5088. Unfortunately, it looks like I don't have permission to push to your PR branch, so I was not able to merge dev-12.0 into this on your behalf to finish it up. If you could do that at your convenience, then I can get this approved and merged!

Thanks again (both for the fix, and for accommodating my various requests :-) )!