code: function nextTick (next, err) {
    return process.nextTick(function () {
      try {
        next(err)
      } catch (e) {
        // istanbul ignore next
        next(e)
      }
    })
  }
docs: Safety wrapper around nextTick
  @api private
  @param {Function} next - next function on the stack
  @param {Object} [err] - error value from previous middleware