pass nil to http.NewRequest if body is nil

github/github.go

@@ -151,8 +151,9 @@ func (c *Client) NewRequest(method, urlStr string, body interface{}) (*http.Requ
 
 	u := c.BaseURL.ResolveReference(rel)
 
-	buf := new(bytes.Buffer)
+	var buf io.ReadWriter
 	if body != nil {
+		buf = new(bytes.Buffer)
 		err := json.NewEncoder(buf).Encode(body)
 		if err != nil {
 			return nil, err

github/github_test.go

@@ -225,6 +225,23 @@ func TestNewRequest_emptyUserAgent(t *testing.T) {
 	}
 }
 
+// If a nil body is passed to github.NewRequest, make sure that nil is also
+// passed to http.NewRequest.  In most cases, passing in io.Reader the returns
+// no content is fine, since there is no difference between an HTTP request
+// body that is an empty string versus one that is not set at all.  However in
+// certain cases, intermediate systems may treat these differently resulting in
+// subtle errors.
+func TestNewRequest_emptyBody(t *testing.T) {
+	c := NewClient(nil)
+	req, err := c.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatalf("NewRequest returned unexpected error: %v", err)
+	}
+	if req.Body != nil {
+		t.Fatalf("constructed request contains a non-nil Body")
+	}
+}
+
 func TestResponse_populatePageValues(t *testing.T) {
 	r := http.Response{
 		Header: http.Header{