After upgrading to 10.0.0-pre02 and building, tons of new - to my eye false - nullable reference warnings on work that was previously working and without warnings.
An example: Student student = studentAdd.Adapt<Student>() suddenly giving nullable reference. I tried to fix with wrapping in an if statement - e.g. if(student is not null){ etc., and sometimes that fixed it, and sometimes the only thing that would fix it was adding the null forgiving exclamation point.
Reverted my 'fixes' and downgraded to 10.0.0-pre01, and warnings went away.