做了个可序列化的类，当xml反序列化的时候，如果哪个节点缺少了，那也不会报错，而是默认的将缺少的节点设为默认值。如何写才能在缺少节点的时候报错？

Public Shared Function Deserialize(ByVal xml As String, ByRef obj As DisbursementList, ByRef exception As System.Exception) As Boolean
        exception = Nothing
        obj = Nothing
        Try
            Dim stringReader As System.IO.StringReader = New System.IO.StringReader(xml)
            Dim xmlTextReader As System.Xml.XmlTextReader = New System.Xml.XmlTextReader(stringReader)
            Dim xmlSerializer As System.Xml.Serialization.XmlSerializer = New System.Xml.Serialization.XmlSerializer(GetType(DisbursementList))
            obj = CType(xmlSerializer.Deserialize(xmlTextReader), DisbursementList)
            Return True
        Catch ex As System.Exception
            exception = ex
            Return False
        End Try
    End Function