public function testFaultyDefinitionReturnsNull()
 {
     $it = new ezcPersistentFindIterator($this->db->prepare("select * from " . $this->db->quoteIdentifier("PO_test")), new ezcPersistentObjectDefinition());
     $this->assertEquals(null, $it->current());
     $this->assertEquals(null, $it->next());
     $this->assertEquals(false, $it->valid());
 }