mod/assign/gradeformat float number formating issue

As a teacher (somebody who can grade) when you are in the submission grade page in the "Grade" part if you enter something like 6,,6 in the "Grade out of 100" field the number get processed as 6 instead of getting an error message.

To get the right behaviour, you must correct the mod/assign/gradeform.php mod_assign_grade_form::validation method changing
line 92: if (unformat_float($data['grade']) === null && (!empty($data['grade']))) {
by
if (!unformat_float($data['grade'], true) && (!empty($data['grade']))) {

With that change, the validation works as expected.

https://github.com/nmoller/moodle/tree/MDL-49323