Fix miscellaneous prod bugs.

impl/prod/datastore_key.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 prod
 
 import (
         ds "github.com/luci/gae/service/datastore"
         "google.golang.org/appengine/datastore"
 )
 
 type dsKeyImpl struct {
         *datastore.Key
 }
 
 var _ ds.Key = dsKeyImpl{}
 
 func (k dsKeyImpl) Parent() ds.Key { return dsR2F(k.Key.Parent()) }
 
 // dsR2F (DS real-to-fake) converts an SDK Key to a ds.Key
 func dsR2F(k *datastore.Key) ds.Key {
+        if k == nil {
+                return nil
+        }
         return dsKeyImpl{k}
 }
 
 // dsF2R (DS fake-to-real) converts a DSKey back to an SDK *Key.
 func dsF2R(k ds.Key) *datastore.Key {
+        if k == nil {
+                return nil
+        }
         if rkey, ok := k.(dsKeyImpl); ok {
                 return rkey.Key
         }
         // we should always hit the fast case above, but just in case, safely round
         // trip through the proto encoding.
         rkey, err := datastore.DecodeKey(ds.KeyEncode(k))
         if err != nil {
                 // should never happen in a good program, but it's not ignorable, and
                 // passing an error back makes this function too cumbersome (and it causes
                 // this `if err != nil { panic(err) }` logic to show up in a bunch of
                 // places. Realistically, everything should hit the early exit clause above.
                 panic(err)
         }
         return rkey
 }
 
 // dsMF2R (DS multi-fake-to-fake) converts a slice of wrapped keys to SDK keys.
 func dsMF2R(ks []ds.Key) []*datastore.Key {
         ret := make([]*datastore.Key, len(ks))
         for i, k := range ks {
                 ret[i] = dsF2R(k)
         }
         return ret
 }