`config.post_body_formatter = :json` and no params causes bad payload with example_request

[jsmestad]

The following example will cause a failure due to sending parameters as:

Processing by Api::PostsController#show as application/json
  Parameters: {"{}"=>nil, "id"=>"0ae45670-7beb-4ff5-aac8-3df1dd4ce601"}

RspecApiDocumentation.configure do |config|
  config.post_body_formatter = :json
end

resource 'Post' do
  delete '/posts/:id' do
    let(:id) { '0ae45670-7beb-4ff5-aac8-3df1dd4ce601' }

    example_request 'delete a post' do
      expect(status).to eql(204)
    end
  end
end

This does not occur when using example alongside do_request, only with example_request due to setting the params as default to {}.

---

Where this happens

I dug into this, and the {"{}"=>nil} portion occurs all the way down in Rack::Utils.parse_query.

irb(main):002:0> require 'rack'
=> true
irb(main):003:0> Rack::Utils.parse_nested_query("{}")
=> {"{}"=>nil}
irb(main):004:0> Rack::Utils.parse_query("{}")
=> {"{}"=>nil}

---

Workaround

    def do_request(extra_params = {})
      @extra_params = extra_params

      params_or_body = nil
      path_or_query = path

      if method == :get && !query_string.blank?
        path_or_query += "?#{query_string}"
      else
        if respond_to?(:raw_post)
          params_or_body = raw_post
        elsif !params.blank? # NOTE: workaround for Rack::Utils.normalize_params bug
          formatter = RspecApiDocumentation.configuration.post_body_formatter
          case formatter
          when :json
            params_or_body = params.to_json
          when :xml
            params_or_body = params.to_xml
          when Proc
            params_or_body = formatter.call(params)
          else
            params_or_body = params
          end
        end
      end

      rspec_api_documentation_client.send(method, path_or_query, params_or_body, headers)
    end