MongoDB C＃驱动程序在First（）调用时崩溃

Question

在查询此文档时，我遇到了最新的MongoDB C＃驱动程序（v1.4.2.4500）崩溃的问题：

{
  "_id" : "4fdfe705b48c6b24dcab994a",
  "CreatedDate" : new Date("6/18/2012 19:42:13"),
  "UpdatedDate" : new Date("6/18/2012 19:42:13"),
  "SiteId" : "4fdfe705b48c6b24dcab9939",
  "ClientId" : "4fdfe705b48c6b24dcab9937",
  "Account" : {
    "UserName" : "blah",
    "Password" : null,
    "PasswordSalt" : null,
  },
  "FbAccount" : {
    "_id" : "838331911",
    "access_token" : "…..",
    "Pages" : []
  }
}

查询：

var q1 = from u in this.Repository.All<User>()
         where u.FbAccount.Id == "832631911"
         select u;

var foo1 = q1.First();

存储库：

public IQueryable<T> All<T>() where T : class, new()
{
    return this.GetQuery<T>().FindAll().AsQueryable();
}

例外：

[NullReferenceException: Object reference not set to an instance of an object.]
   lambda_method(Closure , User ) +137
   System.Linq.WhereEnumerableIterator`1.MoveNext() +155
   System.Linq.Enumerable.First(IEnumerable`1 source) +244
   lambda_method(Closure ) +322
   System.Linq.Queryable.First(IQueryable`1 source) +382
   Framework.Services.ClientService.GetByFacebookUserId(String

     ClientService.cs中的

fbUserId：39

我做错了什么还是这个错误？