Index: ContentLockFilter.php
===================================================================
--- ContentLockFilter.php	(revision 134)
+++ ContentLockFilter.php	(working copy)
@@ -19,10 +19,10 @@
   public function query() {
     $this->ensureMyTable();
     if (empty($this->value)) {
-      $this->query->addWhere($this->options['group'], $this->tableAlias . ".timestamp", "NULL", "=");
+      $this->query->addWhere($this->options['group'], $this->tableAlias . ".timestamp", 0, BooleanOperator::EQUAL);
     }
     else {
-      $this->query->addWhere($this->options['group'], $this->tableAlias . ".timestamp", "NULL", "<>");
+      $this->query->addWhere($this->options['group'], $this->tableAlias . ".timestamp", 0, BooleanOperator::NOT_EQUAL);
     }
   }