impl/memory: Disallow empty namespace.

service/datastore/checkfilter.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 datastore
 
 import (
         "fmt"
 
         "github.com/luci/gae/service/info"
@@ skipping 105 matching lines @@
                 for _, err := range me.(errors.MultiError) {
                         cb(err)
                 }
                 return nil
         }
         return tcf.RawInterface.DeleteMulti(keys, cb)
 }
 
 func applyCheckFilter(c context.Context, i RawInterface) RawInterface {
         inf := info.Get(c)
-        return &checkFilter{i, inf.FullyQualifiedAppID(), inf.GetNamespace()}
+        ns, _ := inf.GetNamespace()
+        return &checkFilter{i, inf.FullyQualifiedAppID(), ns}
 }