Course summary exporter fails with exception. 

It reports that 'showactivitydates' is not defined. 

When i check 'lib/classes/external/exporter.php' it checks for the property for the 'optional' value. 

But in 'course/classes/external/course_summary_exporter.php' is defined as 'null' => NULL_ALLOWED 

therefore it breaks with exception. 

either file must change