diff --git a/protocol/json/server_request.go b/protocol/json/server_request.go
index d23e716..06a5442 100644
--- a/protocol/json/server_request.go
+++ b/protocol/json/server_request.go
@@ -132,7 +132,7 @@ func (src *ServerRequestCodec) NewResponseWithString(reply string, err error) ([
 	res := src.newServerResponse(nil, err)
 
 	r := strings.TrimSpace(reply)
-	if "" != r {
+	if nil == err && "" != r {
 		var i interface{}
 		mErr := json.Unmarshal([]byte(r), &i)
 		if nil != mErr {