我调用API函数“SetSystemTime”设置时间的时候老是出现“未将对象引用设置到对象的实例”的错误。

具体代码如下（我忽略了部分自动生成的代码）：
    '类型的定义
    Public Structure SYSTEMTIME
        Public wYear As Integer
        Public wMonth As Integer
        Public wDayOfWeek As Integer
        Public wDay As Integer
        Public wHour As Integer
        Public wMinute As Integer
        Public wSecond As Integer
        Public wMilliseconds As Integer
    End Structure

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button1.Click
        '定义变量
        Dim T1 As New SYSTEMTIME

        '设置变量
        T1.wYear = 2005
        T1.wMonth = 1
        T1.wDay = 1
        T1.wHour = 12
        T1.wMinute = 1
        T1.wSecond = 2
        '调用API设置时间。（下面这句出错！！！）
        SetSystemTime(T1)
    End Sub

详细错误信息如下：
未处理的“System.NullReferenceException”类型的异常出现在 Test1.exe 中。

其他信息: 未将对象引用设置到对象的实例。