title: C# CacheHelpers NullReference
body: <p>I using for C# in WinForm cache this method</p>
  
  <pre><code>public static bool IsExist(string key)
  {
      return HttpContext.Current.Cache[key] != null;
  }
  </code></pre>
  
  <p>But I have NullReferenceError <strong>return</strong> line.
  How can i solve this problem?
  Thanks</p>