gitlab_project_variable: Allow delete without value (#4150)

* value is not required when state is absent

* fix integration test. missing value

* fix condition

* add changelog fragment

* fail fast

* try required_if on suboptions

* revert

* Update plugins/modules/source_control/gitlab/gitlab_project_variable.py

Co-authored-by: Felix Fontein <felix@fontein.de>

* fix naming in doc

* typo in name

Co-authored-by: Felix Fontein <felix@fontein.de>

tests/integration/targets/gitlab_project_variable/tasks/main.yml

@@ -227,6 +227,7 @@
     vars:
       ACCESS_KEY_ID:
         environment_scope: testing
+        value: checkmode
   register: gitlab_project_variable_state
 
 - name: state must be changed
@@ -242,6 +243,7 @@
     vars:
       ACCESS_KEY_ID:
         environment_scope: testing
+        value: checkmode
   register: gitlab_project_variable_state
 
 - name: state must not be changed
@@ -644,3 +646,51 @@
       - gitlab_project_variable_state.project_variable.untouched|length == 0
       - gitlab_project_variable_state.project_variable.removed|length == 0
       - gitlab_project_variable_state.project_variable.updated|length == 0
+
+- name: throw error when state is present but no value is given
+  gitlab_project_variable:
+    api_url: "{{ gitlab_host }}"
+    api_token: "{{ gitlab_login_token }}"
+    project: "{{ gitlab_project_name }}"
+    variables:
+      - name: delete_me
+  register: gitlab_project_variable_state
+  ignore_errors: yes
+
+- name: verify fail
+  assert:
+    that:
+      - gitlab_project_variable_state.failed
+      - gitlab_project_variable_state is not changed
+
+- name: set a new variable to delete it later
+  gitlab_project_variable:
+    api_url: "{{ gitlab_host }}"
+    api_token: "{{ gitlab_login_token }}"
+    project: "{{ gitlab_project_name }}"
+    purge: True
+    variables:
+      - name: delete_me
+        value: ansible
+  register: gitlab_project_variable_state
+
+- name: verify the change
+  assert:
+    that:
+      - gitlab_project_variable_state.changed
+
+- name: delete variable without referencing its value
+  gitlab_project_variable:
+    api_url: "{{ gitlab_host }}"
+    api_token: "{{ gitlab_login_token }}"
+    project: "{{ gitlab_project_name }}"
+    state: absent
+    variables:
+      - name: delete_me
+  register: gitlab_project_variable_state
+
+- name: verify deletion
+  assert:
+    that:
+      - gitlab_project_variable_state.changed
+      - gitlab_project_variable_state.project_variable.removed|length == 1