SF_10.2 - https://docs.sitefinity.com/for-developers-add-custom-cache-headers

PageOutputCacheStrategyHelper.cs

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Web;

namespace SitefinityWebApp
{
    public static class PageOutputCacheStrategyHelper
    {
        public static bool ContainsKey(this NameValueCollection @this, string key)
        {
            return @this.Get(key) != null
                || @this.Keys.Cast<string>().Contains(key, StringComparer.OrdinalIgnoreCase);
        }
    }
}