[4.0] Don't store a null date but instead store the value null

[wilsonge]

Use the change here #21901 as a baseline for the other core components.

[Quy]

Duplicate #16788?

[richard67]

Yes, I think #16788 can be closed because covered by this here.

The issue is not only with null values, it is in general with datetime columns, also those which shall not be nullable. There are several pull requests made for this and a few more to be done. As soon as all work has finished this issue can be closed.