When using HTTP/1.1, if a BodyPublisher reports an unknown length (-1), the HttpClient will send the request body in Chunked mode. If the publisher publishes an empty byte buffer, the client will generate an empty chunk, which the server will interpret as the end of the request body. Sending an empty chunk can never be valid, unless it's the last body chunk and marks the end of the body.

A new subclass of AbstractNoBody.java could be created to check this scenario. While at it, the tests java/net/httpclient/NoBodyPartOne.java and java/net/httpclient/NoBodyPartTwo.java create a lot of clients and could also make use of HttpClient::close.