reply.trailer() 会导致 204/304 (以及 205 和自动暴露的 HEAD) 失败,因为 transfer-encoding 会在没有 body 的分支中存活

Using `reply.trailer()` together with a status code that cannot carry a body produces broken responses. There are two distinct symptoms, and I'm not sure which behavior is intended, so I'd rather ask before writing a patch.