Fix nil-deref panic from Put.

service/datastore/datastore_test.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.
 
 // adapted from github.com/golang/appengine/datastore
 
 package datastore
 
 import (
         "fmt"
@@ skipping 396 matching lines @@
 
                         Convey("put with non-modifyable type is an error", func() {
                                 cs := CommonStruct{}
                                 So(ds.Put(cs), ShouldErrLike, "invalid Put input type")
                         })
 
                         Convey("struct with no $kind is an error", func() {
                                 s := MGSWithNoKind{}
                                 So(ds.Put(&s), ShouldErrLike, "unable to extract $kind")
                         })
+
+                        Convey("struct with invalid but non-nil key is an error", func() {
+                                type BadParent struct {
+                                        ID     int64 `gae:"$id"`
+                                        Parent *Key  `gae:"$parent"`
+                                }
+                                // having an Incomplete parent makes an invalid key
+                                bp := &BadParent{ID: 1, Parent: ds.MakeKey("Something", 0)}
+                                So(ds.Put(bp), ShouldErrLike, ErrInvalidKey)
+                        })
                 })
 
                 Convey("ok", func() {
                         Convey("[]S", func() {
                                 css := make([]CommonStruct, 7)
                                 for i := range css {
                                         if i == 4 {
                                                 css[i].ID = 200
                                         }
                                         css[i].Value = int64(i)
@@ skipping 826 matching lines @@
                         Convey("extra field with bad type", func() {
                                 type Bad struct {
                                         A int64 `gae:",extra"`
                                 }
                                 So(func() { GetPLS(&Bad{}) }, ShouldPanicLike,
                                         "struct 'extra' field has invalid type int64")
                         })
                 })
         })
 }