I want to filter if the instanceEnd date is null. The RelationPredicateBucket filter does not allow that (see the code in red line). How can i achieve that?. Please advise

filter.PredicateExpression.AddWithOr(ProgramInstanceFields.InstanceEnd > DateTime.Now); filter.PredicateExpression.AddWithOr(ProgramInstanceFields.InstanceEnd== null);

Use a FieldCompareNullPredicate which could be written these ways:

// using the predicate class
bucket.PredicateExpression.Add(new FieldCompareNullPredicate(OrderFields.OrderDate, null));
    
// using natural way
bucket.PredicateExpression.Add((OrderFields.OrderDate==System.DBNull.Value));

// QuerySpec extension methods
.Where(OrderFields.OrderDate.IsNull());

thank you