title: RDLC report doesn't detect NULL values correctly
body: <p>I have a problem with generating .rdlc report. One of the columns has this expression:</p>
  
  <pre><code>IIF(CInt(Fields!MyColumn.Value) = 0 or Fields!MyColumn.Value is nothing,"Unknown",Fields!MyColumn.Value)
  </code></pre>
  
  <p>I've also tried to use that field as a string:</p>
  
  <pre><code>=IIF(IsNothing(Fields!MyColumn.Value) or Fields!MyColumn.Value is nothing,"Unknown",Fields!MyColumn.Value.ToString())
  </code></pre>
  
  <p>When the value of MyColumn is not <code>NULL</code>, the report displays the value properly, but when it is <code>NULL</code> (or 0 when it's converted into int type) the report returns <code>#Error</code>. The weird thing is that when I remove the if function and display only the value of that field, the report displays 0 or blank (it doesn't return the error).
   How can I fix this?</p>