update

myhttp/httpc/httpclient.go

@@ -216,7 +216,10 @@ func (r *Request) Do(method, rawUrl string) (*Response, error) {
 
 	req.URL.RawQuery = query.Encode()
 
+	if r.contentType != "" {
 		req.Header.Set("Content-Type", r.contentType)
+	}
+
 	for k := range r.header {
 		req.Header.Set(k, r.header.Get(k))
 	}