HttpContext.Current.Session is null
<p>I have a WebSite with a custom Cache object inside a class library. All of the projects are running .NET 3.5. 
I would like to convert this class to use Session state instead of cache, in order to preserve state in a stateserver when my application recycles.
However this code throws an exception with "HttpContext.Current.Session is null" when I visit the methods from my Global.asax file. I call the class like this:</p>

<pre><code>Customer customer = CustomerCache.Instance.GetCustomer(authTicket.UserData);
</code></pre>

<p>Why is the object allways null?</p>

<pre><code>public class CustomerCache: System.Web.SessionState.IRequiresSessionState
{
    private static CustomerCache m_instance;

    private static Cache m_cache = HttpContext.Current.Cache;

    private CustomerCache()
    {
    }

    public static CustomerCache Instance
    {
        get
        {
            if ( m_instance == null )
                m_instance = new CustomerCache();

            return m_instance;
        }
    }

    public void AddCustomer( string key, Customer customer )
    {
        HttpContext.Current.Session[key] = customer;

        m_cache.Insert( key, customer, null, Cache.NoAbsoluteExpiration, new TimeSpan( 0, 20, 0 ), CacheItemPriority.NotRemovable, null );
    }

    public Customer GetCustomer( string key )
    {
        object test = HttpContext.Current.Session[ key ];

        return m_cache[ key ] as Customer;
    }
}
</code></pre>

<p>As you can see I've tried to add IRequiresSessionState to the class but that doesn't make a difference.</p>

<p>Cheers
Jens</p>
