Fix optionals when empty

[jbescos]

There was one issue with optionals when the parameter was empty.

[jansupol]

It would be interesting to test @NotNull Integer nullable and @NotNull Optional<Integer> nullable. While the first should fail with bean validation, I'd say the second should not.

[jbescos]

It would be interesting to test @NotNull Integer nullable and @NotNull Optional<Integer> nullable. While the first should fail with bean validation, I'd say the second should not.

Added in this commit: 84198e3