title: Set a database value to null with a SqlCommand + parameters
body: <p>I was previously taught today how to set parameters in a SQL query in .NET in this answer (<a href="https://stackoverflow.com/questions/169359/improving-code-readability-for-sql-commands#169369">click</a>).</p>
  
  <p>Using parameters with values are fine, but when I try to set a field in the database to null I'm unsuccessful. Either the method thinks I am not setting a valid parameter or not specifying a parameter.</p>
  
  <p>e.g.</p>
  
  <pre><code>Dim dc As New SqlCommand("UPDATE Activities SET [Limit] = @Limit WHERE [Activity] = @Activity", cn)
  
  If actLimit.ToLower() = "unlimited" Then
      ' It's not nulling :(
      dc.Parameters.Add(New SqlParameter("Limit", Nothing))
  Else
      dc.Parameters.Add(New SqlParameter("Limit", ProtectAgainstXSS(actLimit)))
  End If
  </code></pre>
  
  <p>Is there something I'm missing? Am I doing it wrong?</p>