Unified Search - Statistics Tracking results in error

Hi,

I am using Unified Search and I want it to appear in the Statistics, so added the Track() method.

IEnumerable _SearchResults = searchClient.UnifiedSearch().For(queryString)
.InField(x => ((BasePageData)x).MetaKeywords)
.InField(x => ((BasePageData)x).MetaTitle)
.InField(x => ((BasePageData)x).MetaDescription)
.Track()
.Filter(x => !x.MatchTypeHierarchy(typeof(ImageData))).Filter(y => !y.MatchTypeHierarchy(typeof(ContainerPage)))
.Take(10).Skip((p - 1) * 10).GetResult(hitSpec, false);

The GetResult method in above statement throws exception "String reference not set to an instance of a String.\r\nParameter name: s"

Stacktrace: 

   at System.Text.Encoding.GetBytes(String s)
   at EPiServer.Find.TrackContext.HashString(String toHash)
   at EPiServer.Find.TrackContext..ctor()
   at EPiServer.Find.SearchExtensions.GetProjectedResult[TResult](ISearch`1 search, SearchContext context)
   at EPiServer.Find.SearchExtensions.GetResult(ITypeSearch`1 search, HitSpecification hitSpecification, Boolean filterForPublicSearch)
   at Trisept.Vax.Epi.ContentSite.Controllers.SearchController.PopulateViewModel(String queryString, VaxBasePageData currentPage, Int32 p) in C:\TFS\Trisept.VAX.Content\Development\Trisept.Vax.Epi\Trisept.Vax.Epi.ContentSite\Controllers\SearchController.cs:line 56
   at Trisept.Vax.Epi.ContentSite.Controllers.SearchController.Index(Nullable`1 p) in C:\TFS\Trisept.VAX.Content\Development\Trisept.Vax.Epi\Trisept.Vax.Epi.ContentSite\Controllers\SearchController.cs:line 40
   at lambda_method(Closure , ControllerBase , Object[] )
   at System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters)
   at System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.b__39(IAsyncResult asyncResult, ActionInvocation innerInvokeState)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResultBase`1.End()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult)
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.b__3d()
   at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass46.b__3f()

If I remove the Track() method, it works fine.

But I need to gather the statistics. Can't figure what I am doing wrong. Please help.

Thank you.

----- Update -----

The above issue occurs only when I am logged in via SAML authenticated user.

Both search and statistics work fine when the user is Epi admin