How do I check if section and subdivision exist inside object's xml?

Question

My function is working but not as I expect it to. The problem is that when Section and Subvision are not found in the object aobjXmlGetStatuteRequestNode xml, I get an error NullReference Exception was unhandled by user code. Object reference not set
to an instance of an object. 
For that reason, because the two elements are optional, I would like to check if they exist before adding their value into the xml inside the object objXmlRequestMessageDoc.
The if statement I used in my function did not work. When it found Section element, it did not check for Subdivision. 
How do I check for both and add them if they exist. If they do not exist, I do not need to do anything and should not throw an error since they are optional.
 Object aobjXmlGetStatuteRequestNode has this xml
<ns:GetStatutesRequest xmlns:ns="http://www.courts.state.mn.us/StatuteService/1.0">
<ns:Statute>
<ns:Chapter>169</ns:Chapter>
<!--Optional:-->
<ns:Section>191</ns:Section>
<!--Optional:-->
<ns:Subdivision>a</ns:Subdivision>
</ns:Statute>
The following output in the objXmlRequestMessageDoc object is correct but this does not work when Section and or Subdivision are not found in the object aobjXmlGetStatuteRequestNode.
<ns:BasicSearchQueryRequest xmlns:ns="http://crimnet.state.mn.us/mnjustice/statute/service/4.0">
<ns1:BasicSearchCriteria xmlns:ns1="http://crimnet.state.mn.us/mnjustice/statute/messages/4.0">
<ns2:Chapter xmlns:ns2="http://crimnet.state.mn.us/mnjustice/statute/4.0"/169</ns2:Chapter>>
<ns2:Section xmlns:ns2="http://crimnet.state.mn.us/mnjustice/statute/4.0"/>191</ns2:Chapter>
<ns2:Subdivision xmlns:ns2="http://crimnet.state.mn.us/mnjustice/statute/4.0"/>a</ns2:Chapter>
</ns1:BasicSearchCriteria>
</ns:BasicSearchQueryRequest>
My Function
Function GetStatutesByChapter(ByVal aobjXmlGetStatuteRequestNode As XmlNode, ByVal aobjXMLNameSpaceManager As XmlNamespaceManager, ByVal aobjBroker As ServiceCatalog.Library.v4.Broker) As XmlDocument
Dim objXmlRequestMessageDoc As XmlDocument
Dim objXmlResponseMessageDoc As XmlDocument
Dim intCount As Integer
aobjBroker.PostMessageWarehouseInformationalMessage("Chapter found.", 1)
objXmlResponseMessageDoc = New XmlDocument
'Add the first element into the document GetStatuteByChapter with its namespace
objXmlResponseMessageDoc.AppendChild(objXmlResponseMessageDoc.CreateElement("BasicSearchQueryResponse", "http://crimnet.state.mn.us/mnjustice/statute/service/4.0"))
'Create the BCA request message
objXmlRequestMessageDoc = New XmlDocument
objXmlRequestMessageDoc.AppendChild(objXmlRequestMessageDoc.CreateElement("ns:BasicSearchQueryRequest", aobjXMLNameSpaceManager.LookupNamespace("ns")))
objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns1:BasicSearchCriteria", aobjXMLNameSpaceManager.LookupNamespace("ns1")))
objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest/ns1:BasicSearchCriteria", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns2:Chapter", aobjXMLNameSpaceManager.LookupNamespace("st")))
objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest/ns1:BasicSearchCriteria", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns2:Section", aobjXMLNameSpaceManager.LookupNamespace("st")))
objXmlRequestMessageDoc.SelectSingleNode("ns:BasicSearchQueryRequest/ns1:BasicSearchCriteria", aobjXMLNameSpaceManager).AppendChild(objXmlRequestMessageDoc.CreateElement("ns2:Subdivision", aobjXMLNameSpaceManager.LookupNamespace("st")))
objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Chapter", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Chapter", aobjXMLNameSpaceManager).InnerText
objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Section", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText
objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Subdivision", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Subdivision", aobjXMLNameSpaceManager).InnerText
'check if there is a section and or subdivision if it is there then set the value
'If Not (aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText) Is Nothing Then
' objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Section", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText
'End If
'check if there is a section and or subdivision if it is there then set the value
aobjBroker.PostMessageWarehouseSnapshot(objXmlRequestMessageDoc.OuterXml, "Request Message", 1)
'Call the BCA service
intCount = 0
'Count how many Statute node found
CType(objXmlResponseMessageDoc.SelectSingleNode("ss:GetStatutesResponse/ss:StatutesXml/ss:Statutes", aobjXMLNameSpaceManager), System.Xml.XmlElement).SetAttribute("totalCount", CStr(intCount))
Return objXmlResponseMessageDoc
End Function

Answer 1

I have resolved this issue by using two if statements as follows
'check if there is a section and or subdivision if it is there then set the value
If Not (aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager) Is Nothing) Then
objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Section", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Section", aobjXMLNameSpaceManager).InnerText
End If
If Not (aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Subdivision", aobjXMLNameSpaceManager) Is Nothing) Then
objXmlRequestMessageDoc.DocumentElement.SelectSingleNode("ns1:BasicSearchCriteria/st:Subdivision", aobjXMLNameSpaceManager).InnerText = aobjXmlGetStatuteRequestNode.SelectSingleNode("ss:Statute/ss:Subdivision", aobjXMLNameSpaceManager).InnerText
End If