code: func (app *Application) handleError(ctx *Context, statusCode int, data ...map[string]interface{}) {
  	ctx.SendStatus(statusCode)
  	handler, ok := app.errorHandler[statusCode]
  	if !ok {
  		defaultErrorHandler(ctx, data...)
  		return
  	}
  	handler(ctx)
  }
docs: // Handles a HTTP Error, if there is a corresponding handler set in the map
  // `errorHandler`, then call it. Otherwise call the `defaultErrorHandler`.