param.go
func GetParam(ctx context.Context, name string) Param {
	n := paramName(name)
	if p, ok := ctx.Value(n).(Param); ok {
		return p
	}
	return ""
}
func GetParam(ctx context.Context, name string) Param {
	n := paramName(name)
	if p, ok := ctx.Value(n).(Param); ok {
		return p
	}
	return ""
}
// GetParam retrieves a param from a context