title: Issue with DBNull when using LINQ to DataSet
body: <p>I've got the following LINQ Statement:</p>
  
  <pre><code>Dim PSNum As Integer = 66 
  Dim InvSeq = (From invRecord In InvSeqDataSet.RptInvSeqDT.AsQueryable() _
                  Where IIf(invRecord.IsPack_NumNull(), False, invRecord.Pack_Num = PSNum) _
                  Select New With _
                  {.Inv = invRecord.Invoice_Num, .Seq = invRecord.Inv_Seq}).FirstOrDefault()
  </code></pre>
  
  <p>invRecord.Pack_Num is a field of type Integer. This means that when I try to access it, if it is DBNull I get a StronglyTypedException. The above code throws this exception. If, however, I remove the "invRecord.Pack_Num = PSNum" and in its place put something like "True", the code works fine. </p>
  
  <p>So I guess my question is, why is that that invRecord.IsPack_NumNull() returns False when the value is in fact DBNull and what can I use as a conditional instead? I've been beating my head against the wall for a while now and I can't find a solution to this problem.</p>