LINQ离开了自己加入

Question

我有LINQ查询如下：

lst_direct_managers = context.sf_guard_user_profile
 .Join(context.sf_guard_user_profile, up => up.user_id, dm => dm.direct_manager_id,
 (up, dm) => new { up, dm })
 .Where(m => m.up.is_gvo == 1)
 .Select(m => new DirectManagerModel
  {
  user_id = m.up.direct_manager_id == null ? 0 : m.up.direct_manager_id,
  dm_full_name = (m.up.first_name + " " + m.up.last_name == null ? "No Direct Manager" : m.up.first_name + " " + m.up.last_name)
  })
  .Distinct()
  .OrderBy(m => m.dm_full_name).ToList();

问题是，如果空值为“No Direct Manager”，它不会返回默认值。你能帮我吗？