anchor.diff:     * passed a non-boolean value.
      */
     Response.expectedBoolean(Request request, String value)
  -    : this(request.id, 'Expected a boolean value, but found "$value"');
  +    : this(request.id, new RequestError(-2, 'Expected a boolean value, but found "$value"'));
   
     /**
      * Initialize a newly created instance to represent an error condition caused
  
positive.code:    * Return a request parsed from the given [data], or `null` if the [data] is
     * not a valid json representation of a request. The [data] is expected to
     * have the following format:
     * 
     *   {
     *     'id': String,
     *     'method': methodName,
  
negative.code:   /**
     * Convert the given [value] to a boolean, or throw a [RequestFailure]
     * exception if the [value] could not be converted.
     *
     * The value is typically the result of invoking either [getParameter] or
     * [getRequiredParameter].
     */
  