code: func isInternal(p *types.Package) (bool, error) {
  	for _, t := range p.Types {
  		for _, member := range t.Members {
  			if member.Name == "TypeMeta" {
  				return !strings.Contains(member.Tags, "json"), nil
  			}
  		}
  	}
  	return false, fmt.Errorf("unable to find TypeMeta for any types in package %s", p.Path)
  }
docs: // isInternal determines whether the given package
  // contains the internal types or not