Question

Can anyone explain why you cannot insert a null object into the ASP.NET cache?

string exampleItem = null;

HttpRuntime.Cache.Insert("EXAMPLE_KEY", 
                        exampleItem, 
                        Nothing,                           
                        DateTime.Now.AddHours(1),
                        System.Web.Caching.Cache.NoSlidingExpiration);

The exception error message states that the “value” object cannot be null. In my application there are valid reasons why we whould want to store a null value in the cache.

Answer 1

Underlying Cache is likely a Hashtable or Dictionary<string, object>, whose getters do not differentiate between no value at that key, or a null value at that key.

Hashtable table = new Hashtable();
object x = table["foo"];
table.Add("foo", null);
object y = table["foo"];
Console.WriteLine(x == y); // prints 'True'

Consider a using placeholder “null” item, similar to DbNull.Value.