How can you add url_posters to dynamic collections?

I having the following dynamic collection that creates collections for people, but it doesn't create posters automatically? How can I add posters?

default_template:
  plex_search:
    any:
      actor: <<value>>

dynamic_collections:
  Actors:         # mapping name does not matter just needs to be unique
    type: actor
    data:
      depth: 5
      minimum: 20