列表作为结构的成员与另一个结构相关联（列表具有另一个结构的对象作为参数）

Question

代码在vb.net中

Structure FeeComponent 
    Public id As Integer
    Public sName As String
    Public oFee As List(new FeeDetail) 
End Structure

另一种结构

Structure FeeDetail

    Public rollNo As Integer
    Public address As String
    Public age As Integer

End Structure

在函数中执行sql查询并将结果存储在Reader中，我想以以下方式向主Structure FeeComponent添加一些详细信息

Dim Retval As New List(Of Idemo.FeeComponent)
Dim Fee As New List(Of Idemo.FeeDetail)

Dim Temp As New Idemo.FeeComponent
Dim Fees As New Idemo.FeeDetail

While Reader.Read

            With Temp
                .id = Reader.Item("id")
                .sName = Reader.Item("Name")
With Fees
                .rollNo = Reader.Item("roll")
    .address = Reader.Item("add")
    .age = Reader.Item("age")
            Temp.Fee.Add(Fees)
        End While

在Temp.Fee.Add（Fees）行上显示错误 如何更正代码我已尽我所能，但我无法更正代码。 我刚开始使用vb，所以请帮忙 错误消息是      System.NullReferenceException：对象引用未设置为对象的实例