golang程序确定用户是否使用代理

I want my golang http client to use a proxy only if the user provides the proxy value.

// Make HTTP GET/POST request
proxyUrl, err := url.Parse(proxy)
tr := &http.Transport{
      DisableKeepAlives: true,
      Proxy:             http.ProxyURL(proxyUrl),
}

The above code always tries to connect through proxy even if the proxy variable is blank.

Thanks for the suggestion. Now I am able to make it work. Below is the modified code.

tr := &http.Transport{}
tr.DisableKeepAlives = true
if len(proxy) != 0 { // Set the proxy only if the proxy param is specified
    proxyUrl, err := url.Parse(proxy)
    if err == nil {
        tr.Proxy = http.ProxyURL(proxyUrl)
    }
 }