Author: Damyon Wiese
MDL-35963: Assignment - do not accept empty submissions
Conflicts:
mod/assign/locallib.php
http://git.moodle.org/gw?p=moodle.git;a=commit;h=85b5e20cdedec890abcd87c393f4b3fd7c8a9451
http://github.com/moodle/moodle/commit/85b5e20cdedec890abcd87c393f4b3fd7c8a9451
+ 2.3 en [submissionempty,mod_assign]