title: The added or subtracted value results in an un-representable datetime
body: <p>I have the following expression to check parameter date values and replace from date if necessary:</p>
  
  <pre class="lang-vb prettyprint-override"><code>=IIF(Parameters!FromDate.Value is nothing, 
      IIF(Parameters!ToDate.Value is nothing,
          DateAdd("d",-30,Now()),
          DateAdd("d",-30,Parameters!ToDate.Value)),
      Parameters!FromDate.Value)
  </code></pre>
  
  <p>Only when the <code>todate</code> is null, an error will get appear:</p>
  
  <blockquote>
    <p>The added or subtracted value results in an un-representable datetime.</p>
  </blockquote>
  
  <p>Did anybody face such a problem?</p>