Fix error message from KeyForObj when passing an invalid struct.

service/datastore/multiarg.go

Index: service/datastore/multiarg.go
diff --git a/service/datastore/multiarg.go b/service/datastore/multiarg.go
index cc1a6726510f6817887f6539a42ba276c780e78b..45e78410e3faef8fee3a9ff758c67ccd93fd6ca0 100644
--- a/service/datastore/multiarg.go
+++ b/service/datastore/multiarg.go
@@ -239,16 +239,13 @@ func multiArgTypeInterface() multiArgType {
 			return newKeyObjErr(aid, ns, slot.Elem().Interface())
 		},
 		getPM: func(slot reflect.Value) (PropertyMap, error) {
-			pls := mkPLS(slot.Elem().Interface())
-			return pls.Save(true)
+			return mkPLS(slot.Elem().Interface()).Save(true)
 		},
 		getMetaPM: func(slot reflect.Value) PropertyMap {
-			pls := getMGS(slot.Elem().Interface())
-			return pls.GetAllMeta()
+			return getMGS(slot.Elem().Interface()).GetAllMeta()
 		},
 		setPM: func(slot reflect.Value, pm PropertyMap) error {
-			pls := mkPLS(slot.Elem().Interface())
-			return pls.Load(pm)
+			return mkPLS(slot.Elem().Interface()).Load(pm)
 		},
 		setKey: func(slot reflect.Value, k *Key) {
 			setKey(slot.Elem().Interface(), k)
@@ -258,37 +255,37 @@ func multiArgTypeInterface() multiArgType {
 
 func newKeyObjErr(aid, ns string, src interface{}) (*Key, error) {
 	pls := getMGS(src)
-	if key, _ := pls.GetMetaDefault("key", nil).(*Key); key != nil {
+	if key, _ := GetMetaDefault(pls, "key", nil).(*Key); key != nil {
 		return key, nil
 	}
 
 	// get kind
-	kind := pls.GetMetaDefault("kind", "").(string)
+	kind := GetMetaDefault(pls, "kind", "").(string)
 	if kind == "" {
 		return nil, fmt.Errorf("unable to extract $kind from %T", src)
 	}
 
 	// get id - allow both to be default for default keys
-	sid := pls.GetMetaDefault("id", "").(string)
-	iid := pls.GetMetaDefault("id", 0).(int64)
+	sid := GetMetaDefault(pls, "id", "").(string)
+	iid := GetMetaDefault(pls, "id", 0).(int64)
 
 	// get parent
-	par, _ := pls.GetMetaDefault("parent", nil).(*Key)
+	par, _ := GetMetaDefault(pls, "parent", nil).(*Key)
 
 	return NewKey(aid, ns, kind, sid, iid, par), nil
 }
 
 func setKey(src interface{}, key *Key) {
 	pls := getMGS(src)
-	if pls.SetMeta("key", key) == ErrMetaFieldUnset {
+	if !pls.SetMeta("key", key) {
 		lst := key.LastTok()
 		if lst.StringID != "" {
-			_ = pls.SetMeta("id", lst.StringID)
+			pls.SetMeta("id", lst.StringID)
 		} else {
-			_ = pls.SetMeta("id", lst.IntID)
+			pls.SetMeta("id", lst.IntID)
 		}
-		_ = pls.SetMeta("kind", lst.Kind)
-		_ = pls.SetMeta("parent", key.Parent())
+		pls.SetMeta("kind", lst.Kind)
+		pls.SetMeta("parent", key.Parent())
 	}
 }