Ability to override the default NullFieldStrategy

My use-case is that I want empty textfields to post an empty String instead of null.
I have implemented a nullfieldstrategy and it can be set on the textfield, but components that create textfields on the fly (eg. Grid) use the default NullFieldStrategy defined in AbstractTextField.
I can't contribute a new "defaults" as that conflicts.

It would be nice to be able to override the strategy defined in AbstractTextField.