micronaut-httpclient-optional

Just a little showcase about the use of java.util.Optional in the Micronaut declarative HTTP client.

The RestClientTest shows how the declarative HTTP client handles optional parameters.

1. No Optional just null values. The client request is as expected. The parameters are not part of the request: GET http://localhost:46893/something
2. The parameter values are supplied as is. The client request is as expected. The parameters are added to the request: GET /something?stringParam=foo&intParam=2
3. Absent parameter values are represented via java.util.Optional.EMPTY. The client request contains a toString-representation of the EMPTY Optional instead of ommitting the parameters: GET /something?stringParam=Optional.empty&intParam=Optional.empty
4. Parameter values are wrapped as java.util.Optional. The client request does contain a toString-representation of the provided Optionals instead of the unwrapped parameter values: GET http://localhost:46893/something?stringParam=Optional%5Bbar%5D&intParam=Optional%5B4%5D

On the server side the wrapping of absent values with Optional works as expected. Absent parameters become Optional.EMPTY and present parameters are wrapped into Optional.