I know the following isn’t really an answer to your question but I do think it’s the proper solution.
I would rather avoid using nullable types altogether. Instead I prefer to rely on default parameters with sensible defaults. So just as an example the joinTo method, it takes loads of parameters but almost all have default value. This just avoids the null checks altogether.
With this approach through my codebases I find the need for such null checks have drastically reduced. Therefor I can live without a special language construct for the times I do run into these kind of issues.