Microsoft ASP.NET Redis Session State throws an exception

Question

When hooking up an ASP.NET website to Azure Redis Cache (but this error also occurs when using a local redis instance) using the Microsoft ASP.NET Redis Session State provider, I get a Null Reference Exception. Why? Google tells me nothing. I have tried using the Russian Redis Session State provider, but that randomly corrupts the session state, so I can't use that either.

This is the stack trace:

[NullReferenceException: Object reference not set to an instance of an object.]
Microsoft.Web.Redis.StackExchangeClientConnection.Eval(String script, String[] keyArgs, Object[] valueArgs) +381
Microsoft.Web.Redis.RedisConnectionWrapper.TryUpdateIfLockIdMatch(Object lockId, ISessionStateItemCollection data, Int32 sessionTimeout) +108
Microsoft.Web.Redis.RedisSessionStateProvider.SetAndReleaseItemExclusive(HttpContext context, String id, SessionStateStoreData item, Object lockId, Boolean newItem) +1280
System.Web.SessionState.SessionStateModule.OnReleaseState(Object source, EventArgs eventArgs) +565
System.Web.SessionState.SessionStateModule.OnEndRequest(Object source, EventArgs eventArgs) +139
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +136
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69

I have no idea where this problem occurs as the stack trace doesn't touch my code, but it occurs on any url hitting my site after I am logged in, yes using forms authentication.

My redis config looks like this:

<sessionState mode="Custom" customProvider="RedisSessionStateStoreProvider">
  <providers>
    <clear />
     <add name="RedisSessionStateStoreProvider" type="Microsoft.Web.Redis.RedisSessionStateProvider, Microsoft.Web.RedisSessionStateProvider, Version=0.4.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" 
          host="*******.redis.cache.windows.net"
          throwOnError = "true" 
          connectionTimeoutInMilliseconds = "5000" 
          retryTimeoutInMilliseconds = "5000" 
          operationTimeoutInMilliseconds = "5000" 
          ssl="true"
          accessKey="*******************************"
          />
  </providers>

... where I have starred out the access key and service uri.

EDIT: I was happy, and thought I had found the solution when I found a post on MSDN Forums (booh!) that dealt with intermittent null reference exceptions where they warned that a nonexistent key being assigned with with a null value will break everything. I found an instance where I was doing this and fixed it,but that didn't actually do the trick and the same problem remains.

I am using Microsoft.Web.RedisSessionStateProvider 0.4.0.0-Pre-121 that allegedly fixes a similar bug

Answer 1

The problem is that I managed to use Null as a key(!!!). What I thought was a properly named constant (like all the other key names) was in fact a variable that was null.

The effects of this mistake differed considerably, so I will post them here if it helps anybody:

Inserting Null as a key caused both the ASP.NET Universal Providers session state provider and RedisAspNetProviders SessionStateProvider to work until the first deserialization after the fatal value with a null key is inserted, after which they blow up with a HttpException (which is correct, probably, although a slightly more helpful error message could be supplied) or an Out Of Memory exception, when I tried storing a List, which is unexpected.

The Microsoft Redis Session State provider blows up with an NRE directly as the idiotic key is inserted and again, us idiots could probably use a better message to save us time.

I tried to use Azure AppFabric as an alternative before I knew what the error was but it was not responding enough to be tested.