Caching abstractions for DI and testing purposes

AspNetCache.cs

namespace IanFNelson.Utilities.Caching
{
    using System;
    using System.Web;
    using System.Web.Caching;

    public class AspNetCache : ICache
    {
        public object Get(string key)
        {
            return HttpRuntime.Cache.Get(key);
        }

        public void Insert(string key, object value)
        {
            if (value == null)
            {
                return;
            }

            HttpRuntime.Cache.Insert(key, value);
        }

        public void Insert(string key, object value, TimeSpan timeToLive, bool slidingExpiration)
        {
            if (value == null)
            {
                return;
            }

            if (slidingExpiration)
            {
                HttpRuntime.Cache.Insert(key, value, null, DateTime.Now.Add(timeToLive), Cache.NoSlidingExpiration);
            }
            else
            {
                HttpRuntime.Cache.Insert(key, value, null, Cache.NoAbsoluteExpiration, timeToLive);
            }
        }

        public int Count
        {
            get { return HttpRuntime.Cache.Count; }
        }
    }
}

ICache.cs

namespace IanFNelson.Utilities.Caching
{
    using System;

    public interface ICache
    {
        void Insert(string key, object value);
        void Insert(string key, object value, TimeSpan timeToLive, bool slidingExpiration);
        object Get(string key);
        int Count { get; }
    }
}

NullCache.cs

namespace IanFNelson.Utilities.Caching
{
    using System;

    public class NullCache : ICache
    {
        public static readonly NullCache Instance = new NullCache();

        public void Insert(string key, object value)
        {
        }

        public object Get(string key)
        {
            return null;
        }

        public void Insert(string key, object value, TimeSpan timeToLive, bool slidingExpiration)
        {
        }

        public int Count
        {
            get { return 0; }
        }
    }
}