func (mi *systemIndexer) BuildIndexes(names ...string) errors.Error {
	return errors.NewSystemNotSupportedError(nil, "BUILD INDEXES is not supported for system datastore.")
}
func (mi *systemIndexer) CreateIndex(name string, equalKey, rangeKey expression.Expressions,
	where expression.Expression, with value.Value) (datastore.Index, errors.Error) {
	return nil, errors.NewSystemNotSupportedError(nil, "CREATE INDEX is not supported for system datastore.")
}