Supposing a type with the following definition:

I would expect Optional.empty() to generate no validation errors, because the value is not present. Certainly that's the way other constraints work. Unfortunately, what I get instead is:

'must not be blank'

It's pretty clear why this is happening:

OptionalValueExtractor.java

...and since null isn't a valid value, it of course fails the validation. Any null-failing validator would complain at that point.

A more idiomatic way to deal with optionals would be something like:

OptionalValueExtractor.java

...which would only call the receiver if it was present. However, that's only if the value was present, which is a behavior change, so I'm unsure of all the ramifications of that.