code: func (g *metadataGraph) init(root *api.PrefixMetadata) {
  	if root != nil && root.Prefix != "" {
  		panic("the root node metadata should have empty prefix")
  	}
  	g.root = &metadataNode{
  		acls: make([]*packageACL, len(legacyRoles)),
  		md:   root,
  	}
  }
docs: // init initializes the root node.