Git commits in Moodle 3.5.3 by Guillermo Alvarez

commit 5b75de57f203a31d6527b6da4e0c8d32bbe33b90
Author: Guillermo Alvarez <guillermo.alvarez@blackboard.com>
Date:   Sat, 25 Aug 2018 01:40:06 +0800
Tag:    v3.5.3

MDL-63231 filepicker: Skype validation for null values