Improve unhandled error handling in prod mode

router.go

@@ -368,8 +368,8 @@ func (p *ControllerRegistor) ServeHTTP(rw http.ResponseWriter, r *http.Request)
 			if _, ok := err.(middleware.HTTPException); ok {
 				// catch intented errors, only for HTTP 4XX and 5XX
 			} else {
-				errstr := fmt.Sprint(err)
-				if handler, ok := middleware.ErrorMaps[errstr]; ok && ErrorsShow {
+				if ErrorsShow {
+					handler := p.getErrorHandler(fmt.Sprint(err))
 					handler(rw, r)
 				} else {
 					if !RecoverPanic {
@@ -865,6 +865,24 @@ Admin:
 	}
 }
 
+// there always should be error handler that sets error code accordingly for all unhandled errors
+// in order to have custom UI for error page it's necessary to override "500" error
+func (p *ControllerRegistor) getErrorHandler(errorCode string) func(rw http.ResponseWriter, r *http.Request) {
+	handler := middleware.SimpleServerError
+	ok := true
+	if errorCode != "" {
+		handler, ok = middleware.ErrorMaps[errorCode]
+		if !ok {
+			handler, ok = middleware.ErrorMaps["500"]
+		}
+		if !ok || handler == nil {
+			handler = middleware.SimpleServerError
+		}
+	}
+
+	return handler
+}
+
 //responseWriter is a wrapper for the http.ResponseWriter
 //started set to true if response was written to then don't execute other handler
 type responseWriter struct {