code: func (rwt *RWTree) Load(version int64, overwriting bool) error {
  	const errHeader = "RWTree.Load():"
  	if version <= 0 {
  		return fmt.Errorf("%s trying to load from non-positive version %d", errHeader, version)
  	}
  	err := rwt.tree.Load(version, overwriting)
  	if err != nil {
  		return fmt.Errorf("%s loading version %d: %v", errHeader, version, err)
  	}
  	// Set readTree at commit point == tree
  	rwt.ImmutableTree, err = rwt.tree.GetImmutable(version)
  	if err != nil {
  		return fmt.Errorf("%s loading version %d: %v", errHeader, version, err)
  	}
  	return nil
  }
docs: // Tries to load the execution state from DB, returns nil with no error if no state found