code: public static Role of(String value) {
      checkNotNull(value);
      if (!value.contains("/")) {
        value = ROLE_PREFIX + value;
      }
      return new Role(value);
    }
docs: Returns a new role given its string value.
  
  <p>If the value contains no slash character ({@code '/'}), the prefix {@code "roles/""} is
  prepended. This slightly simplifies usage for <a
  href="https://cloud.google.com/iam/docs/understanding-roles">predefined roles</a>. For <a
  href="https://cloud.google.com/iam/docs/creating-custom-roles">custom roles</a>, call this
  method with the fully-qualified name, eg {@code "projects/XXX/roles/YYY"}.
  
  @param value the string value for the role
  @see <a href="https://cloud.google.com/iam/docs/viewing-grantable-roles">Viewing the Grantable
  Roles on Resources</a>