Fix error message from KeyForObj when passing an invalid struct.

service/datastore/pls_impl.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.
 
 // HEAVILY adapted from github.com/golang/appengine/datastore
 
 package datastore
 
 import (
         "fmt"
@@ skipping 334 matching lines @@
                 }
         }
         if needKind {
                 if _, ok := p.c.byMeta["kind"]; !ok {
                         ret["$kind"] = []Property{MkPropertyNI(p.getDefaultKind())}
                 }
         }
         return ret
 }
 
-func (p *structPLS) GetMetaDefault(key string, def interface{}) interface{} {
-        return GetMetaDefaultImpl(p.GetMeta, key, def)
-}
-
 func (p *structPLS) SetMeta(key string, val interface{}) (err error) {
         if err = p.Problem(); err != nil {
                 return
         }
         idx, ok := p.c.byMeta[key]
         if !ok {
                 return ErrMetaFieldUnset
         }
         st := p.c.byIndex[idx]
         if !st.canSet {
@@ skipping 237 matching lines @@
                 switch val {
                 case "on", "On", "true":
                         return true, nil
                 case "off", "Off", "false":
                         return false, nil
                 }
                 return nil, fmt.Errorf("Toggle field has bad/missing default, got %q", val)
         }
         return nil, fmt.Errorf("helper: meta field with bad type/value %s/%q", t, val)
 }