Fix usage example and ensure that systemd_unit is defined

README.md

@@ -165,7 +165,7 @@ conf:
   Network:
     Address:
       - 192.168.0.2/24
-      - 192.168.0.3/24 
+      - 192.168.0.3/24
 ```
 
 The list items are are converted into duplicated keys:
@@ -230,8 +230,12 @@ This role can be included in another role along these lines (this has been based
   ansible.builtin.include_role:
     name: systemd
     tasks_from: unit_present.yml
+  loop: "{{ docker_systemd_units }}"
+  loop_control:
+    loop_var: systemd_unit
+    label: "{{ systemd_unit.name }}"
   vars:
-    systemd_units:
+    docker_systemd_units:
       - name: docker-compose
         state: enabled
         files:

meta/argument_specs.yml

@@ -94,7 +94,7 @@ argument_specs:
     options:
       systemd_unit:
         type: dict
-        required: false
+        required: true
         description: A single systemd unit.
         options:
           files:

tasks/unit_present.yml

@@ -20,6 +20,11 @@
         var: systemd_unit
         verbosity: 2
 
+    - name: The systemd_unit variable needs to be defined
+      ansible.builtin.assert:
+        that:
+          - systemd_unit is defined
+
     - name: Include the package install tasks when defined
       ansible.builtin.include_tasks: pkg_present.yml
       loop: "{{ systemd_unit.pkgs }}"