fix: no need to send content-type header if no header sent (#91)

* fix: no need to send content-type header if no header sent

close: #76

* Update gerrit.go

Co-authored-by: Andy Grunwald <andygrunwald@gmail.com>

gerrit.go

@@ -244,7 +244,11 @@ func (c *Client) NewRequest(method, urlStr string, body interface{}) (*http.Requ
 	// Request compact JSON
 	// See https://gerrit-review.googlesource.com/Documentation/rest-api.html#output
 	req.Header.Add("Accept", "application/json")
-	req.Header.Add("Content-Type", "application/json")
+
+	// No need to send the content type if there is no content
+	if body != nil {
+		req.Header.Add("Content-Type", "application/json")
+	}
 
 	// TODO: Add gzip encoding
 	// Accept-Encoding request header is set to gzip