Steps to reproduce:

1. Create a trigger, and add tag with no value, for example: 'Database:'
   
2. Set this trigger in status 'Problem'
3. Go to: Monitoring -> Problems
4. Click on 'Customize table' and enable 'Tag value' column

Result:
Tag value is displayed as an empty rectangle:

In compact view:

Expected:
Empty tag value shouldn't be displayed at all