Fixes nil proxy url behavior

Author: seans3

client.go

@@ -426,8 +426,9 @@ func (d *Dialer) proxyNetDial(req *http.Request, netDial netDialerFunc) (netDial
 	if err != nil {
 		return nil, err
 	}
+	// Request should not be proxied; use originial dial function.
 	if proxyURL == nil {
-		return nil, errors.New("generated proxy url is nil")
+		return netDial, nil
 	}
 	if proxyURL.Scheme == "http" && d.NetDialTLSContext != nil {
 		return nil, errors.New("dial TLS function set for dialing non-HTTPS proxy")

client_test.go

@@ -46,12 +46,6 @@ func TestProxyNetDialErrors(t *testing.T) {
 			proxyFn:  nil,
 			errorMsg: "proxy url function is nil",
 		},
-		"proxy generating nil URL is error": {
-			proxyFn: func(req *http.Request) (*url.URL, error) {
-				return nil, nil
-			},
-			errorMsg: "generated proxy url is nil",
-		},
 		"proxy URL generator returning error is error": {
 			proxyFn: func(req *http.Request) (*url.URL, error) {
 				return nil, errors.New("error generating proxy url")