Git commits in Moodle 3.8.0 by Michael Aherne

commit bf93e13abe880b95ba712a97c552b51a65f0b2a2
Author: Michael Aherne <michael.aherne@strath.ac.uk>
Date:   Mon, 18 Mar 2019 18:30:48 +0800
Tag:    v3.8.0-beta

MDL-65096 docs: Use static return type in persistent