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当我运行我的程序时，代码正确捕获了超时异常，但随后我收到一条弹出消息：

Microsoft.VisualBasic.dll 中出现了“System.NullReferenceException”类型的第一次机会异常

还这样说：

未设置对象变量或 With 块变量。

这是我的代码：

Dim rt As String = ""
Dim out As String
Dim wRequest As WebRequest
Dim wResponse As WebResponse
Dim SR As StreamReader
Dim time As Date

time = Now()

Try
    wRequest = WebRequest.Create(Address)
    wRequest.Timeout = 10000
    wResponse = wRequest.GetResponse
    SR = New StreamReader(wResponse.GetResponseStream)
    rt = SR.ReadToEnd
    SR.Close()
Catch wex As System.Net.WebException
    If wex.Status = WebExceptionStatus.Timeout Then
        MessageBox.Show("Could not establish a connection to the selected exchange server.", "Connection Timed Out", MessageBoxButtons.OK, MessageBoxIcon.Warning)
    End If
End Try
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