[djthorpe]

NewRequest and NewRequestEx return a payload that's an io.Reader with nothing to read. DoWithContext passed it to http.NewRequestWithContext as the request body, and because the body wasn't nil, every request without a payload was sent with Content-Type: application/json. That included GET, HEAD, POST and DELETE. Some servers refuse a GET or HEAD with a content type.

DoWithContext now sends a request without a body when its payload is one of go-client's own requests with no buffer, so it has no content type. JSON payloads, and other payload types such as streaming and multipart, are unchanged.

Tests: TestDoContentType in do_test.go checks that GET, HEAD, POST and DELETE without a payload arrive with no Content-Type, no length and no body, and that a JSON request still sends application/json and its body. It fails without the fix.

go test ./... passes, apart from pkg/homeassistant, whose tests call a live server (hay.mutablelogic.com) that doesn't resolve from here. They fail the same way on main.

[Copilot]

🟢 Approval recommended

No active review issues block the change to omit bodies and automatic Content-Type headers from payload-free requests.

No open issues 🎉

What changed in this PR

This PR fixes how the client sends its own payload-free requests, omitting the body and automatic Content-Type header so servers do not reject otherwise valid GET or HEAD requests.

Changes:

• Pass a nil body for built-in requests with no buffer, leaving JSON and other payload types unchanged.
• Add regression tests for payload-free GET, HEAD, POST, and DELETE requests, plus JSON payload preservation.

File	Description
do_test.go	Tests absent content type and empty bodies, and verifies JSON requests remain intact.
client.go	Uses a nil body for built-in requests without a payload buffer.

_{Review effort: Balanced}