title: Checking for DBNull throws a StrongTypingException
body: <p>I am using a dataset to pull data from a DB. One of the fields in a row is <code>NULL</code>. I know this. However, the following vb.net code throws a <code>StrongTypingException</code> (in the autogenerated get_SomeField() method in the dataset designer):</p>
  
  <p><pre><code>If Not IsDBNull(aRow.SomeField) Then
  'do something
  End If</pre></code></p>
  
  <p>According to documentation and <a href="https://stackoverflow.com/questions/222834/handling-dbnull-data-in-vb-net">this question</a> it should be fine.</p>
  
  <p>edit: <code>If aRow.SomeField is DBNull.Value Then</code> also returns the same error. Argh.</p>