title: Troubles with IsNull Crystal Reports
body: <p>I'm using Crystal Reports 12.3 and Peachtree Accounting 2012 to manage some database. My task now is simply make a report that contains customers that have not placed orders in last 30 days. I'm new to it so I'm asking your help.</p>
  
  <p>My first trying was to use this formula (I'm doing all my stuff in Formula Editor -> Record Selection): </p>
  
  <p><code>not ({Customers.LastInvoiceDate} in Aged0To30Days)</code></p>
  
  <p>Everything seems to be fine except null values. I need to include in report records with null values. So I rewrite the formula to:</p>
  
  <p><code>not ({Customers.LastInvoiceDate} in Aged0To30Days) OR IsNull({Customers.LastInvoiceDate})</code></p>
  
  <p>But in Peachtree Accounting 2012 I'm seeing a customer with a blank <code>LastInvoiceDate</code> field which is not in report. </p>
  
  <p>Is there some kind of bug in my last formula? Or is there some "other" black values for DateTime type?</p>