salt/states/grains/init.sls

{# ensure that grains pillar exists -#}
{%- if pillar['roles'] is defined %}
set-roles:
  grains.present:
    - name: roles
    - force: true
    - value: [{% for role in pillar['roles'] %}{{role}},{% endfor %}]
{% else %}
set-roles:
  grains.absent:
    - name: roles
{%- endif -%}