Does RequestBuilder::send always return an Err if server responds with a status code between 400 and 599?

[ghost]

There are 2 things that ALL HTTP clients do that I absolutely hate:

1. Automatically override content-type without documenting (in worst cases they might even set user-agent to their library name).
2. Treat certain status codes as errors. Why would you do that?

Anyhow, please clarify.