Author: Paul Holden
MDL-66392 analytics: make model output directory default to empty.
Falling back to path within $CFG->dataroot/models.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=0efc7095e3936faf78dd22f4f37a6c0faf24538b
http://github.com/moodle/moodle/commit/0efc7095e3936faf78dd22f4f37a6c0faf24538b
+ 3.9 en [modeloutputdirwithdefaultinfo,core_analytics]