code: func (ctx *Context) Query(key string, index ...int) (string, error) {
  	if val, ok := ctx.Request.Form[key]; ok {
  		if len(index) == 1 {
  			return val[index[0]], nil
  		}
  		return val[0], nil
  	}
  	return "", errors.New("Query key not found")
  }
docs: // Query method retrieves the form data, return empty string if not found.