datastore/key.go
func NewIncompleteKey(c context.Context, kind string, parent *Key) *Key {
	return NewKey(c, kind, "", 0, parent)
}
func NewIncompleteKey(c context.Context, kind string, parent *Key) *Key {
	return NewKey(c, kind, "", 0, parent)
}
// NewIncompleteKey creates a new incomplete key.
// kind cannot be empty.