NullRefException in
   в IdeaBlade.Linq.PredicateBuilder.FilterQuery(IQueryable baseQuery, IPredicateDescription predicateDescription)
   в IdeaBlade.Windows.ObjectDataSource.GetFilteredQuery()
   в IdeaBlade.Windows.ObjectDataSource.LoadView()
   в IdeaBlade.Windows.ObjectDataSource.LoadCore()
   в IdeaBlade.Windows.ObjectDataSource.Load()
   в CivilizationWeb.Views.TaskList.OnNavigatedTo(NavigationEventArgs e)
   в System.Windows.Controls.Page.InternalOnNavigatedTo(NavigationEventArgs e)
   в System.Windows.Navigation.NavigationService.RaiseNavigated(Object content, Uri uri, Page existingContentPage, Page newContentPage)
   в System.Windows.Navigation.NavigationService.CompleteNavigation(DependencyObject content)
   в System.Windows.Navigation.NavigationService.ContentLoader_BeginLoad_Callback(IAsyncResult result)

//souce:IdeaBlade.Linq.PredicateBuilder
public static IQueryable FilterQuery(IQueryable baseQuery, IPredicateDescription predicateDescription)
{
    Type genericArgument = TypeFns.GetGenericArgument(baseQuery.GetType());
    Expression expression = Expression.Call(typeof(Queryable), "Where", new Type[] { genericArgument }, new Expression[] { Expression.Constant(baseQuery), predicateDescription.ToLambdaExpression() }); //predicateDescription _CAN_ be null
    return baseQuery.Provider.CreateQuery(expression);
}

// source: IdeaBlade.Windows.ObjectDataSource
private IPredicateDescription GetQueryFilter()
{
    try
    {
        List<PredicateDescription> list = new List<PredicateDescription>();
        foreach (FilterDescriptor descriptor in this.FilterDescriptors)
        {
            PredicateDescription item = descriptor.ToPredicateDescription(this.Query.ElementType);
            if (item != null)
            {
                list.Add(item);
            }
        }
        if (list.Count > 0)
        {
            return PredicateBuilder.And(list.ToArray());
        }
        return null; ///!!!!
    }
    catch (Exception exception)
    {
        TraceFns.WriteLine("Filters ignored: " + exception.Message);
        return null;
    }
}