Developer credits
Git commits in Moodle 3.1.0 by Kevin Wiliarty
commit 393890e1682955cbbc73e9f6d7340d97747ca2e1 Author: Kevin Wiliarty <kevin.wiliarty@gmail.com> Date: Wed, 27 Apr 2016 01:18:43 +0800 Tag: v3.1.0-rc2 MDL-54620 ratings: display '0' when aggregate = 0