Default render for empty string should be '-' in entities lists

[Archidoit]

Default render for empty string should be '-' in entities list (and not empty space)

Reproducible Steps

In entities list, empty string should be displayed as '-' and not as empty space.

Exemples:

• in Incident Response overview > tasks list, the 'assignees' field is displayed as empty space if there are no assignees :
  

• in 'triggers and digests' of group overview
  

• in members list of group overview
  

• in triggers list