Milo: Fix frontpage bug

milo/appengine/frontend/frontpage.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package frontend
 
 import (
         "github.com/luci/luci-go/server/router"
         "github.com/luci/luci-go/server/templates"
 
@@ skipping 14 matching lines @@
                         return err
                 }
                 ch <- func() (err error) {
                         mBuildbucket, err = buildbucket.GetAllBuilders(c.Context)
                         return err
                 }
         })
 
         fp.CIServices = append(fp.CIServices, *mBuildbucket)
         fp.CIServices = append(fp.CIServices, *mBuildbot)
+        errMsg := ""
+        if err != nil {
+                errMsg = err.Error()
+        }
         templates.MustRender(c.Context, c.Writer, "pages/frontpage.html", templates.Args{
                 "frontpage": fp,
-                "error":     err.Error(),
+                "error":     errMsg,
         })
 }
 
 func frontpageTestData() []common.TestBundle {
         data := &templates.Args{
                 "frontpage": resp.FrontPage{
                         CIServices: []resp.CIService{
                                 {
                                         Name: "Module 1",
                                         BuilderGroups: []resp.BuilderGroup{
@@ skipping 16 matching lines @@
                 },
                 "error": "couldn't find ice cream",
         }
         return []common.TestBundle{
                 {
                         Description: "Basic frontpage",
                         Data:        *data,
                 },
         }
 }