I got an error when comparing non-nullable type to null

Question

I've got problems at this line:

int? nextLevel = (from p in cd.Objective
                  where p.Parent_ObjectiveID == null
                  select p.ObjectiveID).Max() + 1;

The error specifies:

The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type.

How can I fix it?

UPDATE:

But p.Parent_ObjectiveID is int? datatype. It can be null.

Answer 1

The objectiveID is of type which is not nullable. So whats the point of checking it for NULL type? You never can assign a null value to a non nullable value. May be use objectiveID? instead..

Answer 2

Basically, p.Parent_ObjectiveID cannot be null , (ie a "non-nullable" type). So there is no need to check if it is a null or not.

So to fix it, get rid of the where part, or change it from null , to an System.Int32 value.