When a Google Calendar is linked to a Moodle Calendar using an iCal URL, changing an event's description to empty in Google Calendar does not update the event description in Moodle if it already contains text.

Recreation:

• Link a Google Calendar to your Moodle Calendar
• Set the "Event Type" to "Site Wide"
• Create an event in the linked Google Calendar with a description
• Update the Moodle Calendar by going to Calendar > Manage Subscriptions and change the interval in which the calendar is updated to any option
• Check the event appears in the Moodle Calendar
• Now delete the event description in Google Calendar and click "Save"
• Update the Moodle Calendar again
• Go back to the Moodle Calendar - The description remains unchanged

Possible location of issue:
./calendar/lib.php in function calendar_add_icalendar_event line 3008
$result = array_diff((array) $eventrecord, (array) $updaterecord);

In PHP documentation: "Compares array against one or more other arrays and returns the values in array that are not present in any of the other arrays"

If $eventrecord->description = "Description of event"
And $updaterecord->description = ""
Then $result->description = "Description of event"
When it should be $result->description = ""