I am using the xmltextwriter and having issues with opening tags not showing if the field is blank

here is the start of my code

Code:
   Dim strFilePath As String = Server.MapPath("../test.xml")
        Dim utf8 As Encoding = New UTF8Encoding(False)
        Dim objWriter As XmlTextWriter = New XmlTextWriter(strFilePath, New UTF8Encoding(False))

        ' start writing the XML document
        objWriter.WriteStartDocument()

      
        Try
            conn.Open()
            myreader = cmd.ExecuteReader

         
            objWriter.WriteStartElement("testfile")

            While myreader.Read

                ' output the first "product" element
                objWriter.WriteStartElement("product", Nothing)
                objWriter.WriteElementString("Id", myreader("rvid").ToString)
                objWriter.WriteElementString("Class", myreader("RVClass").ToString)
                objWriter.WriteElementString("Manu", myreader("rvmanu").ToString)
                objWriter.WriteElementString("Model", myreader("rvmake") & " " & myreader("rvmodel"))
                objWriter.WriteElementString("Year", myreader("rvyear").ToString)
                objWriter.WriteElementString("Price", myreader("rvcashprice").ToString)
                objWriter.WriteElementString("NU", myreader("rvnu").ToString)
                objWriter.WriteElementString("SCapacity", myreader("rvcapacity").ToString)
                objWriter.WriteElementString("Fuel", myreader("rvfuel").ToString)
                objWriter.WriteElementString("Length", myreader("rvlenft").ToString)
                objWriter.WriteElementString("Air", myreader("rvair").ToString)
                objWriter.WriteElementString("Awnings", myreader("rvawnings").ToString)
Thats not all of it.. but what happens is if it is blank value

Then i get this, as you see fuel has no opening tags, and the company i am supplying to needs these.

<Price>0.0000</Price>
<NU>U</NU>
<SCapacity>0</SCapacity>
<Fuel />
<Length>0</Length>


What can i do to make this work how i want? I though the .tostring woudl fix it but it didnt.

Thanks