Author: Mark Nelson
MDL-42764 core: added missing string definition
Also changed the string index so it was not
vague. The index 'emailempty' appears as if it
could belong to a validation method for a form.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=4c86ca66667ae801d93405066f26202dd34ceb76
http://github.com/moodle/moodle/commit/4c86ca66667ae801d93405066f26202dd34ceb76
+ 3.4 en [emailuserhasnone,core]