code: function payloadAsBufferOrString (payload) {
    var returnValue = payload
    if (!Buffer.isBuffer(returnValue)) {
      if (typeof payload === 'object') {
        returnValue = JSON.stringify(payload)
      } else if (typeof payload !== 'string') {
        returnValue = '' + payload
      }
    }
    return returnValue
  }
docs: Convert the supplied payload to a Buffer or String. If the parameter is a
  already a Buffer or String, the text parameter is returned as-is. If the
  parameter is anything else, e.g., an Object, a String representation of
  the parameter is returned.
  @private
  @param {(Object|String)} payload - The text to convert.
  @returns {(Buffer|String)} Buffer or string representation of the payload.