code: func (r *Router) InternalServerError(handlers ...Handler) {
  	handlers = validateAndWrapHandlers(handlers)
  	r.internalServerError = func(c *Context, err error) {
  		c.index = 0
  		c.handlers = handlers
  		c.Map(err)
  		c.run()
  	}
  }
docs: // InternalServerError configurates handler which is called when route handler returns
  // error. If it is not set, default handler is used.
  // Be sure to set 500 response code in your handler.