Filter on empty value in a dynamic field

[fpaco]

Hello,

I have created a drop-down dynamic field in which I enabled the empty selectable value. Now my customers want to be able to filter ticket on all values : the one I manually added plus the empty one. Even though the empty value is selectable in a field, it is not selectable for a search or for a filter on the ticket view.

Does anyone know how to enable that?

Thanks for your help,

Paco