Servers cannot deserialize empty primitive optional values sent by Feign clients

[pkoenig10]

What happened?

A service is exposing an endpoint with an OptionalLong header parameter. A Conjure Feign client calls this endpoint with an OptionalLong.empty() value and receives a 400 because this parameter fails to deserialize with NumberFormatException.

What did you want to happen?

The request from the client should have succeeded.

Details

This is related to #790.

Requests with Optional<T> parameters work because Jersey will return null if an exception is thrown while deserializing an empty string.

[carterkozak]

The conjure spec requires optional headers to be absent from the request to deserialize into an empty optional, otherwise we would not be able to differentiate between a present optional of an empty string, and and absent optional.