postfix: don't differentiate between undefined and empty alias lists

postfix/tasks/main.yml

@@ -130,7 +130,7 @@
   template:
     src: virtual.j2
     dest: /etc/postfix/virtual
-  when: virtual_aliases is defined or postfix_virtual_domains|count > 0
+  when: virtual_aliases|default([])|count > 0 or postfix_virtual_domains|count > 0
   notify:
     - postmap virtual
   tags:

postfix/templates/aliases.j2

-{% for alias in system_aliases %}
+{% for alias in system_aliases|default([]) %}
 {% if alias.src is string %}
 {{ alias.src }}: {{ alias.dest if alias.dest is string else alias.dest|join(', ') }}
 {% else %}

postfix/templates/main.cf.j2

@@ -98,7 +98,7 @@ tls_ssl_options = NO_COMPRESSION
 
 alias_maps = cdb:/etc/aliases
 alias_database = cdb:/etc/aliases
-{% if virtual_aliases is defined or postfix_virtual_domains|count > 0 %}
+{% if virtual_aliases|default([])|count > 0 or postfix_virtual_domains|count > 0 %}
 virtual_alias_maps = cdb:/etc/postfix/virtual
 {% endif %}
 

postfix/templates/virtual.j2

@@ -4,7 +4,7 @@ hostmaster@{{ domain }} {{ adminaddr }}
 abuse@{{ domain }} {{ adminaddr }}
 {% endfor %}
 
-{% for alias in virtual_aliases %}
+{% for alias in virtual_aliases|default([]) %}
 {% if alias.src is string %}
 {{ alias.src }} {{ alias.dest if alias.dest is string else alias.dest|join(', ') }}
 {% else %}