'Null' value displayed when no repeat frequency is selected

[ilieandriuta]

STEPS TO REPRODUCE

1. Login with Admin
2. Go to Flash Messages App from Apps Panel
3. Click on 'Create'
4. Type a name for the new flash message
5. Click 'Create'
6. Select a Start Date (e.g. Now)
7. Click in Groups field and type a group name (e.g. XWikiAllGroup)
8. Select Repeat: Yes
9. Select 'Repeat Interval': Daily, Weekly, Monthly, Yearly
10. Observe the 'Repeat Summary' field

EXPECTED RESULTS

In the 'Repeat Interval' is displayed 'Every - days', or weeks/months/years due tot the fact that the 'Repeat frequency' is not selected (has the value '---').

ACTUAL RESULTS

Instead, when 'Repeat frequency' is not selected (has the default value) is displayed 'Every null days/weeks/months/years'.

If both 'Repeat interval' and 'Repeat frequency' have '---' (default value), in 'Repeat Summary' is displayed 'Every null flash.repeat.summary.' In this situation, it could have the value 'Please select a Repeat Interval and Frequency first.'

Environment: Windows 10 Pro 64 bit, Chrome 70, using a local instance XWiki 10.8.1 on PostgreSQL 10