code: function foundCircularReference (keyPath, $refs, options) {
    $refs.circular = true;
    if (!options.dereference.circular) {
      throw ono.reference("Circular $ref pointer found at %s", keyPath);
    }
    return true;
  }
docs: Called when a circular reference is found.
  It sets the {@link $Refs#circular} flag, and throws an error if options.dereference.circular is false.
  
  @param {string} keyPath - The JSON Reference path of the circular reference
  @param {$Refs} $refs
  @param {$RefParserOptions} options
  @returns {boolean} - always returns true, to indicate that a circular reference was found