set user agent header only if non-empty

github/github.go

@@ -165,7 +165,9 @@ func (c *Client) NewRequest(method, urlStr string, body interface{}) (*http.Requ
 	}
 
 	req.Header.Add("Accept", mediaTypeV3)
-	req.Header.Add("User-Agent", c.UserAgent)
+	if c.UserAgent != "" {
+		req.Header.Add("User-Agent", c.UserAgent)
+	}
 	return req, nil
 }
 

github/github_test.go

@@ -211,6 +211,20 @@ func TestNewRequest_badURL(t *testing.T) {
 	testURLParseError(t, err)
 }
 
+// ensure that no User-Agent header is set if the client's UserAgent is empty.
+// This caused a problem with Google's internal http client.
+func TestNewRequest_emptyUserAgent(t *testing.T) {
+	c := NewClient(nil)
+	c.UserAgent = ""
+	req, err := c.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatalf("NewRequest returned unexpected error: %v", err)
+	}
+	if _, ok := req.Header["User-Agent"]; ok {
+		t.Fatal("constructed request contains unexpected User-Agent header")
+	}
+}
+
 func TestResponse_populatePageValues(t *testing.T) {
 	r := http.Response{
 		Header: http.Header{