Graph of Report "Course Overview" is not show

The graph of "Course Overview" report is not show.

With the Debug enabled, the following message is show:

<br />
<b>Notice</b>: Undefined variable: course in <b>.../moodle/admin/report/courseoverview/reportsgraph.php</b> on line <b>15</b><br />
<br />
<b>Notice</b>: Trying to get property of non-object in <b>.../moodle/admin/report/courseoverview/reportsgraph.php</b> on line <b>15</b><br />

Solution:

Before the code on the line 15 of this file, include this code:

$course = get_site();

And graphs works fine!