code: function getErrorMessage (err, status, env) {
    var msg
  
    if (env !== 'production') {
      // use err.stack, which typically includes err.message
      msg = err.stack
  
      // fallback to err.toString() when possible
      if (!msg && typeof err.toString === 'function') {
        msg = err.toString()
      }
    }
  
    return msg || statuses[status]
  }
docs: Get message from Error object, fallback to status message.
  
  @param {Error} err
  @param {number} status
  @param {string} env
  @return {string}
  @private