fix #1070 (#1389)

* fix #1070

* test: add more tests

rest/httpx/responses.go

@@ -14,13 +14,17 @@ var (
 )
 
 // Error writes err into w.
-func Error(w http.ResponseWriter, err error) {
+func Error(w http.ResponseWriter, err error, fns ...func(w http.ResponseWriter, err error)) {
 	lock.RLock()
 	handler := errorHandler
 	lock.RUnlock()
 
 	if handler == nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
+		if len(fns) > 0 {
+			fns[0](w, err)
+		} else {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+		}
 		return
 	}