Identity datetime? field doesn't allow null

I've extended IdentityUser with a ApplicationUser class with several custom fields to match the AspNetUsers table I have in a SQL Server DB. A couple of them are defined in SQL as, for example: MyDate datetime2 null. In my ApplicationUser class it would be: datetime? MyDate;.

Now, the only way I can set it to null is with a T-SQL command separate from Entity Framework and if it is null, my application throws an exception reading it from the DB.

I do admit that it was erroneously declared as datetime MyDate in ApplicationUser for awhile before I updated it to match the DB. Is this the cause of the problems I'm seeing? If so, how do I get my ApplicationUser to match the current DB schema?

Here's the exception:

01/10/19 17:14:47.034 ERROR 114 MyApp.Global - Exception occurred: 
System.Web.HttpUnhandledException (0x80004005): Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.Data.ConstraintException: The 'MyDateUtc' property on 'ApplicationUser' could not be set to a 'null' value. You must set this property to a non-null value of type 'System.DateTime'. 
   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper.ErrorHandlingValueReader`1.GetValue(DbDataReader reader, Int32 ordinal)
   at lambda_method(Closure , Shaper )
   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper.HandleEntityAppendOnly[TEntity](Func`2 constructEntityDelegate, EntityKey entityKey, EntitySet entitySet)
   at lambda_method(Closure , Shaper )
   at System.Data.Entity.Core.Common.Internal.Materialization.Coordinator`1.ReadNextElement(Shaper shaper)
   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper`1.SimpleEnumerator.<MoveNextAsync>d__4.MoveNext()

Here's the ApplicationUser class (trimmed a bit) and supporting classes:

public class ApplicationUser : IdentityUser<long, CustomUserLogin, CustomUserRole, CustomUserClaim>
{
    [Key]
    [DatabaseGeneratedAttribute(DatabaseGeneratedOption.None)]
    public override long Id
    {
        get { return base.Id; }
        set { base.Id = value; }
    }

    public DateTime? MyDateUtc { get; set; }

    public ClaimsIdentity GenerateUserIdentity(UserManager<ApplicationUser, long> manager)
    {
        // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
        var userIdentity = manager.CreateIdentity(this, DefaultAuthenticationTypes.ApplicationCookie);
        // Add custom user claims here
        return userIdentity;
    }

    public Task<ClaimsIdentity> GenerateUserIdentityAsync(ApplicationUserManager manager)
    {
        return Task.FromResult(GenerateUserIdentity(manager));
    }
}

public class ApplicationDbContext : IdentityDbContext<ApplicationUser, CustomRole, long, CustomUserLogin, CustomUserRole, CustomUserClaim>
{
    public ApplicationDbContext() : base("MyDbConnection")
    {
    }

    public static ApplicationDbContext Create()
    {
        return new ApplicationDbContext();
    }
}

public class CustomUserRole : IdentityUserRole<long> { }
public class CustomUserClaim : IdentityUserClaim<long> { }
public class CustomUserLogin : IdentityUserLogin<long> { }

public class CustomRole : IdentityRole<long, CustomUserRole>
{
    public CustomRole() { }
    public CustomRole(string name) { Name = name; }
}

public class CustomUserStore : UserStore<ApplicationUser, CustomRole, long, CustomUserLogin, CustomUserRole, CustomUserClaim>
{
    public CustomUserStore(ApplicationDbContext context) : base(context)
    {
    }
}

public class CustomRoleStore : RoleStore<CustomRole, long, CustomUserRole>
{
    public CustomRoleStore(ApplicationDbContext context) : base(context)
    {
    }
}

DateTime is a Struct and as such, is a value type. This means it the cannot be set to null.

You may solve your problem with the help of the nullable operator. Using a question mark (?) after the type or using the generic style Nullable.

Nullable <DateTime> MyDateUtc;

or

DateTime? MyDateUtc;

You should check your DbContext class just in case your class' property is being set as required. More info here