It would be nice to bring support of JDK8's Optional class.

Before JDK8, using Guava Optional class doesn't go very well with bean validation while I guess the user should be able to make the choice of using null values + @NotNull, or using Optional<Value>, but still be able to validate the non-null value

I guess it is a bit related to this:
https://hibernate.atlassian.net/browse/BVAL-202