Suggestion: Use default request body if request body is null when POST, PUT, PATCH...

[10000-ki]

Hello there,

First of all
I'm using this library well in my project. Thank you!!.

I found an issue that it doesn't allow empty request body except GET

### Send request with no request's body
POST https://httpbin.org/post

> {%
  client.test("Response is ok", function() {
    client.assert(response.status === 200, "Response status is not ok");
  });
%}

Perhaps this is the effect of the OkHttpRequest library.

• OkhttpRequestExecutor.kt

• Request.kt

However it doesn't matter in IntelliJ, and it works well.

How about using default request body if request doesn't have a request body when http method is post, put, patch..

// example
private fun getRequestBody(request: Request): RequestBody? {
        val body = request.body?.toRequestBody() ?: request.createMultipartRequestBody()

        if (HttpMethod.requiresRequestBody(request.method.name) && body == null) {
            return "{}".toRequestBody()
        }

        return body
}

so if you don't mind i can raise a PR soon

with pleasure