docs: function getResponseMessage( err, req, env ) {
    var content_type = req.get( 'content-type' ) || ''
    var message = err.toString()
  
    if ( content_type.indexOf( 'application/json' ) !== -1 ) {
      message = {
        error: {
          code: err.code || null,
          errorCode: err.errorCode || null,
          message: err.toString(),
          status: err.status || null,
          statusCode: err.statusCode || 500
        }
      }
    } else if ( env === 'development' ) {
      message = '<pre>' + err.stack
    }
  
    return message
  }