RavenDB 索引错误

我刚刚开始使用 Raven，我创建的索引始终无法索引任何内容。我在 Raven 服务器上发现了很多如下所示的错误：

{
    Index: "HomeBlurb/IncludeTotalCosts",
    Error: "Cannot implicitly convert type 'double' to 'int'. An explicit conversion exists (are you missing a cast?)",
    Timestamp: "2012-01-14T15:40:40.8943226Z",
    Document: null
}

我创建的索引如下所示：

public class HomeBlurb_IncludeTotalCosts : AbstractIndexCreationTask<MPDocument, HomeBlurb_IncludeTotalCosts.ReduceResult>
{
    public class ReduceResult 
    {
        public string Name { get; set; }
        public string Constituency { get; set; }
        public decimal AmountPaid { get; set; }
    }

    public HomeBlurb_IncludeTotalCosts()
    {
        Map = mps => from mp in mps
                            from expense in mp.Expenses
                            select new
                            {
                                mp.Name,
                                mp.Constituency,
                                AmountPaid = expense.AmountPaid ?? 0M
                            };

        Reduce = results => from result in results
                            group result by new { result.Name, result.Constituency } 
                            into g
                            select new
                            {
                                g.Key.Name,
                                g.Key.Constituency,
                                AmountPaid = g.Sum(x => x.AmountPaid)
                            };
    }
}

该索引由 Raven 创建（通过 Raven Studio 查看），看起来不错。

真正让我困惑的是我使用的文档不包含任何双精度或整数，我存储的唯一数字是小数。

可能是什么原因导致了这个问题？

问题出在这一行：

              AmountPaid = g.Sum(x => x.AmountPaid)

将其替换为：

              AmountPaid = g.Sum(x => (double)x.AmountPaid)