this is for v9251...
EditDoubleNotNull, when field is cleared backcolor is changed, but when
setting focus to another control, there is nothing in it(it's null) - is this a bug?
Or is there an easy way to config it so default value for it is 0?
It is no a bug. Ctrl::Accept would stop there with error (e.g. on pressing OK button).
I think it would not be a good idea to consider empty field equal to 0.