Enum defined as IsOptional cannot be queried for null values

Question

I have defined an Enum property on an Entity via Fluent API as IsOptional. The database reflects the IsOptional as it shows it as a nullable type. When I attempt to query this Entity property for null values I get the following error:

The 'UserType' property on 'Group' could not be set to a 'null' value. 
You must set this property to a non-null value of type 'UserType'.

The query is as follows:

var groups = (from g in db.Groups
              let reqs = from r in db.Requests 
              where r.Id == requestId from gg in r.Groups select gg.Id                                  
              where g.ContentArea.Id == db.Requests.FirstOrDefault(o => o.Id == requestId).ContentArea.Id
              where !reqs.Contains(g.Id)
              where (g.UserType == db.Requests.FirstOrDefault(r => r.Id == requestId).User.UserType || g.UserType == (UserType?)null)
              select g).ToList();

and the part that specifically breaks is after the OR statement

g.UserType == (UserType?)null

I've tried to compare g.UserType to null, set an instance of UserType? nullType = null and compared that but nothing seems to work. It seems to be a shortcoming of EF. Any suggestions?

EDIT: Included the entire query as requested.

Answer 1

The problem is not in the structure of the statement, it's in the entities EF tries to materialize. Group has a property UserType that's not nullable. But in the database it is nullable and some of the returned records have null values for it.

So you either have to make the property nullable:

UserType? UserType { get; set; }

or make sure that the statement doesn't return null values.