InfoPath Dev

 the below is the code i have written to retrieve the sharepoint list values, the values are pulling when no null values are there, if the null(empty) value in the list, throwing exception error. 

 xiRepatingTableDescriptions.Current.SelectSingleNode("my:HDDTemp_RowExported", ns).SetValue("Export Complete")
                                    'Set CAML query to insert new values to the 'Product Descriptions' sharepoint list
                                    DataSources(ExportedSharepointlistname).QueryConnection.Execute()
                                    xiPreviousProductDescriptions = Me.DataSources(ExportedSharepointlistname).CreateNavigator().Select("/dfs:myFields/dfs:dataFields/dfs:Product_Descriptions", Me.NamespaceManager)
                                                                      
                                     While (xiPreviousProductDescriptions.MoveNext())
                                       previousSKU = xiPreviousProductDescriptions.Current.SelectSingleNode("@SKU", ns).ToString()
                                               

can anyone help me on this?

How about something like this:

    While (xiPreviousProductDescriptions.MoveNext())
       Dim prevSkuNode as XPathNavigator = xiPreviousProductDescriptions.Current.SelectSingleNode("@SKU", ns)
       If prevSkuNode IsNot Nothing
          previousSKU = prevSkuNode.Value