XML deserialization and missing fields - how to know if someting is missing?

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VB

XML

Hello,
I have some class and wish to store it in XML file and then read it again. So I use XMLSerialiser, and it works fine, but I don't know how to handle situation if someone change XML file.
E.g. my class Save method produse this XML file

<?xml version="1.0" encoding="utf-8"?>
<Data xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <FileName>test.txt</FileName>
  <SheetName>List</SheetName>
  <FirstRow>0</FirstRow>
</Data>

if someone delete all elements inside and leave only

<?xml version="1.0" encoding="utf-8"?>
<Data xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
</Data>

my code don't get any error or any exception, but leave properties which are missing in XML file uninitialized.
I want to know about such events, how can I achieve this?

Code:

<XmlRootAttribute("Data")> _
Public Class SeriazableClass
#Region "Members"
    Private _FileName As String
    Private _SheetName As String
    Private _FirstRow As Integer
#Region "Properties"
    Property FileName() As String
        Get
            Return _FileName
        End Get
        Set(ByVal value As String)
            _FileName = value
        End Set
    End Property
    Property SheetName() As String
        Get
            Return _SheetName
        End Get
        Set(ByVal value As String)
            _SheetName = value
        End Set
    End Property
    Property FirstRow() As Integer
        Get
            Return _FirstRow
        End Get
        Set(ByVal value As Integer)
            _FirstRow = value
        End Set
    End Property
#End Region
#End Region
#Region "Methods"
    Public Sub New()
    End Sub
    Public Sub Save()
        Dim serializer As New XmlSerializer(GetType(SeriazableClass))
        Dim writer As New StreamWriter("test.xml")
        serializer.Serialize(writer, Me)
        writer.Close()
    End Sub
    Public Shared Function Read() As SeriazableClass
        Dim serializer As New XmlSerializer(GetType(SeriazableClass))
        Try
            Dim reader As New StreamReader("test.xml") 'there is possible file-not-found
            Try
                Read = serializer.Deserialize(reader) 'there is possible invalid-xml
            Finally
                reader.Close()
            End Try
        Catch ex As Exception
            MsgBox(ex.Message & vbCrLf & " during reading", , "Error reading xml file")
            Read = New SeriazableClass
        Finally
        End Try
    End Function
#End Region
End Class