
Some servers will return an error response if a `Content-Length` header isn't included in a `POST` request, so this adds it to the `post_args` array when `post_form` or `post_json` are used.
Some servers will return an error response if a `Content-Length` header isn't included in a `POST` request, so this adds it to the `post_args` array when `post_form` or `post_json` are used.