var aaa = _dbContext.IdentityAppUsers
    .Where(x => x.Uuid == 'ABC')
    .SelectMany(l => l.OrganisationOrganisationUsers)
    .Select(x => 
      x.Organisation!.OrganisationStandards
      .Select(od => od.Uuid).First());

由于OrganisationStandards是一个空集合，我预计上面的查询将在First（）方法上抛出一个no sequence异常，但它没有。
有什么想法吗
生成的sql就像

SELECT (
    SELECT o1.uuid
    FROM query.organisation_standard AS o1
    WHERE o0.id = o1.organisation_id
    LIMIT 1)
FROM query.identity_app_user AS i
INNER JOIN query.organisation_organisation_user AS o ON i.id = o.user_id
INNER JOIN query.organisation_organisation AS o0 ON o.organisation_id = o0.id
WHERE i.uuid = 'ABC'