Developer credits
Git commits in Moodle 3.1.5 by Tim Lock
commit dfbbb39a25618a49974fa914a7678b68cfe5e738 Author: Tim Lock <tim@netspot.com.au> Date: Tue, 17 Jan 2017 09:50:26 +0800 Tag: v3.1.5 MDL-57668 mod_assign: Fix optional_param() form processing