code: function arity(min, max = Number.MAX_SAFE_INTEGER) {
    return (req, res, next) => {
      const foundArity = parsePath(req).length-1;
      if (foundArity < min ) {
        next(new ModofunError(400, 'InvalidInput',
          `This operation requires ${min} parameters. Received ${foundArity}.`));
      } else if (foundArity > max ) {
        next(new ModofunError(400, 'InvalidInput',
          `This operation doesn't accept more than ${max} parameters. Received ${foundArity}.`));
      } else {
        next();
      }
    }
  }
docs: Utility middleware to enforce a minimum number of parameters.
  Accepts an extra argument for an optional maximum number.
  @public