json.id                collaborator.id

json.actor_id          collaborator.actor_id
json.actor_name        collaborator.actor_name
json.actor_type        collaborator.actor_type
json.avatar            avatar_url(collaborator.actor)
json.actor_path        participant_path(collaborator.actor)

json.project_id        collaborator.project_id
json.role              collaborator.role