title: Testing for a valid date in a oracle procedure's parameter
body: <p>Oracle 8 here.</p>
  
  <p>When passing a date to a procedure, I can pass a '' and nothing is thrown.  </p>
  
  <p>Testing for <code>MYDATE := ''</code> doesn't eval to true.  Nor does <code>LENGTH &lt; 1</code>.  DBMS_OUTPUT shows nothing coming through the parameter.</p>
  
  <p>Trying to pass <code>'01-30-2009' (instead of 30-JAN-2009)</code> throws an invalid date error.  </p>
  
  <p>How is passing a zero length string valid?</p>
  
  <p>How do I test for a valid date?</p>