Set additional services is failing due to missing variable about ansible-gitlab-runner HOT 8 CLOSED

ansible [core 2.12.2]
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.8/site-packages/ansible
  ansible collection location = /root/.ansible/collections:/usr/share/ansible/collections
  executable location = /usr/bin/ansible
  python version = 3.8.12 (default, Sep 16 2021, 10:46:05) [GCC 8.5.0 20210514 (Red Hat 8.5.0-3)]
  jinja version = 2.10.3
  libyaml = True

    - file:
        path: /tmp/foo1
        state: touch
    - blockinfile:
        dest: "/tmp/foo1"
        content: "{{ lookup('template', 'config.runners.docker.services.j2') if nondefinedvariable is defined }}"
        state: "{{ 'present' if nondefinedvariable is defined else 'absent' }}"
        marker: "# {mark} runners.docker.services"
        insertafter: EOF
      check_mode: no

# ansible-playbook --connection=local --inventory inventory.yml t.yml

PLAY [runner] *********************************************************************************************************************************************************************************************************************************

TASK [Gathering Facts] ************************************************************************************************************************************************************************************************************************
ok: [gitlab.blabla]

TASK [file] ***********************************************************************************************************************************************************************************************************************************
changed: [gitlab.blabla]

TASK [blockinfile] ****************************************************************************************************************************************************************************************************************************
fatal: [gitlab.blabla]: FAILED! => {"msg": "The task includes an option with an undefined variable. The error was: the inline if-expression on line 1 evaluated to false and no else section was defined.\n\nThe error appears to be in '/tmp/gitlab-ansible-playbook/t.yml': line 6, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n        state: touch\n    - blockinfile:\n      ^ here\n"}

PLAY RECAP ************************************************************************************************************************************************************************************************************************************
gitlab.blabla       : ok=2    changed=1    unreachable=0    failed=1    skipped=0    rescued=0    ignored=0   

# cat t.yml
- hosts: runner
  tasks:
    - file:
        path: /tmp/foo1
        state: touch
    - blockinfile:
        dest: "/tmp/foo1"
        content: "{{ lookup('template', 'config.runners.docker.services.j2') if nondefinedvariable is defined }}"
        state: "{{ 'present' if nondefinedvariable is defined else 'absent' }}"
        marker: "# {mark} runners.docker.services"
        insertafter: EOF
      check_mode: no

ansible [core 2.12.2]
  config file = None
  configured module search path = ['/root/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python3.9/dist-packages/ansible
  ansible collection location = /root/.ansible/collections:/usr/share/ansible/collections
  executable location = /usr/local/bin/ansible
  python version = 3.9.2 (default, Feb 28 2021, 17:03:44) [GCC 10.2.1 20210110]
  jinja version = 3.1.2
  libyaml = True