Optional headers with an empty value are converted to the empty string

What happened?

I have an endpoint method with an optional argument annotated by @HeaderParam:

@GET
@Path("/doStuff")
String doStuff(@HeaderParam("value") Optional<String> value);

I passed it the value Optional.empty() via a JaxRsClient:

MyService service = JaxRsClient.create(...
service.doStuff(Optional.empty())

However, the implementation of doStuff receives the value Optional.of(""), rather than Optional.empty().

There is a failing test case to show this at https://github.com/palantir/http-remoting/compare/develop...DoronShapiro:optional-header-tests.

This behavior happens because the implementation of Java8OptionalAwareContract serializes empty headers as an empty string, but when they are deserialized by the Java8OptionalParamConverterProvider, it is assumed that the value will be null if empty (and that the empty string represents a non-empty value).

What did you want to happen?

The server should receive a value of Optional.empty() for the header argument.

One solution is for the client to not include the header at all if its value is Optional.empty().