static_websites: Define static_websites as empty list by default

roles/static_websites/defaults/main.yml

@@ -39,4 +39,4 @@ static_websites_default_traefik_certresolver: letsencrypt_http
 #      tmpfs: - List tmpfs definitions like the example below that should be added to the container (optional)
 #        "/tmp/nginx-cache": 1M
 # See the README for an example
-# static_websites: []
+static_websites: []

roles/static_websites/tasks/main.yml

@@ -36,7 +36,7 @@
     group: 'root'
     validate: python2 -m compose -f %s config -q
   when:
-    - static_websites is defined
+    - static_websites | length > 0
   tags:
     - docker
     - deploy_sites
@@ -50,6 +50,6 @@
     remove_orphans: yes
   become: true
   when:
-    - static_websites is defined
+    - static_websites | length > 0
   tags:
     - deploy_sites