ProductsOrderedCondition.cs

public class ProductsOrderedCondition<T> : TypedQueryableStringOperatorCondition<T, IndexedContact> 
    where T : VisitorRuleContext<IndexedContact>
{
    protected override Expression<Func<IndexedContact, bool>> GetResultPredicate(T ruleContext)
    {
        string fieldName = "contact.SampleOrder.Skus";

        return this.GetCompareExpression((Expression<Func<IndexedContact, string>>)(c => c[fieldName]), this.Value);
    }
}