Distinguish nil values in the database

[maxdml]

Use a special marker __DBOS_NIL to represent nil values in the database instead of storing as NULL.

[kraftp]

Is this necessary? What problem is it solving? I thought we decided not to do this. The problem it could solve is UI confusion between nil and empty, but I don't see the code for that here and I'm not even sure it's a problem in Go because Go returns (nil, err) and such.

[maxdml]

Is this necessary? What problem is it solving? I thought we decided not to do this. The problem it could solve is UI confusion between nil and empty, but I don't see the code for that here and I'm not even sure it's a problem in Go because Go returns (nil, err) and such.

Yeah it just solves the problem of what value gets stored in the database. For the UI, we do return empty strings if nil to the client (it expects empty strings for nil). No impact on the programming model - that's why the serialization tests did not change.