Here is a quick hint on how to use Propel and its Criteria class to generate queries that need to have Null or Not Null in WHERE clauses:
<?php
$c = new Criteria();
$c->add(TablePeer::TABLE_ID, null, Criteria::NOT_EQUAL);
// this is the same as above
$c = new Criteria();
$c->add(TablePeer::TABLE_ID, null, Criteria::ISNOTNULL);
// ======================================
// for equality checking do this:
$c = new Criteria();
$c->add(TablePeer::TABLE_ID, null);
// or
$c = new Criteria();
$c->add(TablePeer::TABLE_ID, null, Criteria::EQUAL);
// or
$c = new Criteria();
$c->add(TablePeer::TABLE_ID, null, Criteria::ISNULL);
?>
