Fix error message from KeyForObj when passing an invalid struct.

filter/dscache/ds.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package dscache
 
 import (
         "time"
 
         ds "github.com/luci/gae/service/datastore"
@@ skipping 69 matching lines @@
                                 }
                         } else {
                                 p.lme.Assign(i, err)
                                 if err != ds.ErrNoSuchEntity {
                                         return // aka continue to the next entry
                                 }
                         }
 
                         if toSave != nil {
                                 if shouldSave { // save
-                                        expSecs := metas.GetMetaDefault(i, CacheExpirationMeta, CacheTimeSeconds).(int64)
+                                        mg := metas.GetSingle(i)
+                                        expSecs := ds.GetMetaDefault(mg, CacheExpirationMeta, CacheTimeSeconds).(int64)
                                         toSave.SetFlags(uint32(ItemHasData))
                                         toSave.SetExpiration(time.Duration(expSecs) * time.Second)
                                         toSave.SetValue(data)
                                 } else {
                                         // Set a lock with an infinite timeout. No one else should try to
                                         // serialize this item to memcache until something Put/Delete's it.
                                         toSave.SetFlags(uint32(ItemHasLock))
                                         toSave.SetExpiration(0)
                                         toSave.SetValue(nil)
                                 }
@@ skipping 29 matching lines @@
                 if err == nil {
                         err = txnState.apply(d.supportContext)
                 }
                 return err
         }, opts)
         if err == nil {
                 txnState.release(d.supportContext)
         }
         return err
 }