OkHttp transport rejects body-less POST/PUT/PATCH with IllegalArgumentException

[OmarAlJarrah]

Problem

RequestAdapter.adapt passes a null body straight to OkHttp:

val okhttpBody = request.body?.let { toOkHttpBody(it) }
builder.method(request.method.method, okhttpBody)   // RequestAdapter.kt:55-56

For POST/PUT/PATCH, OkHttp's Request.Builder.method throws IllegalArgumentException("method X must have a request body") when the body is null. A body-less POST is valid HTTP, and nothing stops a caller from building one: Request.RequestBuilder.build() only requires method and url (Request.kt:254-257) and Method carries no body-requirement metadata. Because the failure is an IllegalArgumentException (not an IOException), it also bypasses retry. The JDK transport does not have this problem, so behaviour differs across transports.

Proposed change

When body == null and the method permits/requires a body (POST/PUT/PATCH), pass an empty request body instead of null. Audit the JDK transport for parity (BodyPublishers.noBody()).

Acceptance

• Body-less POST/PUT/PATCH dispatches through the OkHttp transport
• Parity test across OkHttp and JDK transports
• Regression test for the previously-throwing path

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Priority: high · Effort: small