EntityFramework-Effort: DatabaseGeneratedOption.Computed always causes null

I have a column like the following:

    [Column, DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime? LastModified { get; set; }

and a SQL trigger that sets it as expected. Entity framework expects the database to set this property and reads it back after each insert and update. Effort always reports this as null. That is:

    var entity = new MyEntity { LastModified = DateTime.Now };
    dbContext.MyEntities.Add(entity);
    dbContext.SaveChanges();
    Assert.NotNull(entity.LastModified);

fails where dbContext is a DbContext created from a transcient Effort DbConnection.

I would like some mechanism to get around this. Perhaps an EntityWithComputedColumnInserting event and an EntityWithComputedColumnUpdating event for allowing users to handle the computing of computed columns. Say using an EventArgs similar to the following:

    public class ComputedColumnEventArgs : EventArgs
    {
        public Type EntityType { get; }
        public string ComputedColumnName { get; }
        public object ComputedValue { get; set; }
    }

I could then make an event handler like the following in my test class:

    private void ComputeLastModified(object sender, ComputedColumnEventArgs e)
    {
        if (e.EntityType = typeof(MyEntity) 
            && e.ComputedColumnName == nameof(MyEntity.LastModified))
        {
            e.ComputedValue = _now;
        }
    }