Add default for new parameter of header() in renderer

renderer.php

@@ -38,9 +38,10 @@ class tool_lifecycle_renderer extends plugin_renderer_base {
     /**
      * Write the page header
      *
+     * @oaram string optional page title.
      * @return string
      */
-    public function header($title) {
+    public function header($title = null) {
         global $OUTPUT, $PAGE;
         echo $OUTPUT->header();
         if ($title) {