如何将Type.IsGenericTypeDefinition设置为true

我有一个具有BeginDate和EndDate属性的许多类，我想构建一个泛型方法，该方法将一个对象返回为相同类型但具有BeginDate=EndDate的List。

例如：

项目开始日期=2011-05-01，项目结束日期=2011-05-03

结果必须是

项目1.开始日期=2011-05-01，项目1.结束日期=2011-05-01

项目2.开始日期=2011-05-02，项目2.结束日期=2011-05-02

项目3.开始日期=2011-05-03，第3项结束日期=2011-05-03

我尝试了以下代码

<Extension()> _
        Public Function GetRatesPerDay(Of T As Class)(ByVal oldRatesList As List(Of T)) As List(Of T)
            If oldRatesList Is Nothing OrElse oldRatesList.Count = 0 Then
                Return New List(Of T)
            End If
            Dim ratesInDays As New List(Of T)
            Dim oldBeginDate = oldRatesList.Where(Function(D) D IsNot Nothing).Min(Function(D) GetType(T).GetProperty("BeginDate", GetType(DateTime)).GetValue(D, Nothing))
            Dim oldEndDate = oldRatesList.Where(Function(D) D IsNot Nothing).Max(Function(D) GetType(T).GetProperty("EndDate", GetType(DateTime)).GetValue(D, Nothing))
            Dim currentDay As DateTime = oldBeginDate
            Dim typeArgs() As Type = {GetType(DateTime), GetType(DateTime), GetType(Nullable(Of Double)), GetType(String), GetType(HUMPSBaseClasses.RoomRateType)}
            Dim constructed As Type = GetType(T).MakeGenericType(typeArgs)
            While currentDay <= oldEndDate
                Dim dayRate = (From D In oldRatesList _
                                Where D IsNot Nothing _
                                AndAlso currentDay >= GetType(T).GetProperty("BeginDate", GetType(DateTime)).GetValue(D, Nothing) _
                                AndAlso currentDay <= GetType(T).GetProperty("EndDate", GetType(DateTime)).GetValue(D, Nothing) _
                                Select New With {.NightRate = GetType(T).GetProperty("NightRate", GetType(Nullable(Of Double))).GetValue(D, Nothing), _
                                                 .RatePlanID = GetType(T).GetProperty("RatePlanID", GetType(System.String)).GetValue(D, Nothing), _
                                                 .RoomRateType = GetType(T).GetProperty("RoomRateType", GetType(HUMPSBaseClasses.RoomRateType)).GetValue(D, Nothing) _
                                                 }).SingleOrDefault()
                If dayRate IsNot Nothing Then
                    Dim tempRate As Object = Activator.CreateInstance(constructed)
                    tempRate = New With {.BeginDate = currentDay, _
                                             .EndDate = currentDay, _
                                             .NightRate = dayRate.NightRate, _
                                             .RatePlanID = dayRate.RatePlanID, _
                                             .RoomRateType = dayRate.RoomRateType}
                    ratesInDays.Add(tempRate)
                End If
                currentDay = currentDay.AddDays(1)
            End While
            Return ratesInDays
        End Function

但是我遇到了一个问题，我的类的Type.IsGenericTypeDefinition是假的。

我怎样才能将其设置为真？