code: func (b *Builder) Close() error {
  	err := b.compileFrom(0)
  	if err != nil {
  		return err
  	}
  	root := b.unfinished.popRoot()
  	rootAddr, err := b.compile(root)
  	if err != nil {
  		return err
  	}
  	return b.encoder.finish(b.len, rootAddr)
  }
docs: // Close MUST be called after inserting all values.