Ansible raises an exception when running tasks with loops calling super()

[Diego]

Running a simple playbook with loops with Ansible 2.5.1 (Ubuntu package version is '2.5.1+dfsg-1ubuntu0.1+esm2', and this is important because in previous version this error was not raised) in Ubuntu 18.04 raises this error:

PLAY [Ansible Bug]
TASK [Show Ansible Version]
fatal: [localhost]: FAILED! => {"msg": "the field 'args' has an invalid value ([]), and could not be converted to an dict.The error was: super() takes at least 1 argument (0 given)\n\nThe error appears to have been in '/home/user/ansible-tests/ansible-bug/bug.yaml': line 12, column 7, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n tasks:\n - name: Show Ansible Version\n ^ here\n"}
        to retry, use: --limit @/home/user/ansible-tests/ansible-bug/bug.retry

PLAY RECAP
localhost : ok=0 changed=0 unreachable=0 failed=1

The playbook contains:

- name: Ansible Bug
  hosts: localhost
  connection: local
  gather_facts: no
  vars:
    test_items:
      - a
      - b
  tasks:
    - name: Show Ansible Version
      debug:
        msg: "Ansible Version: {{ ansible_version }} - {{ item }}"
      loop: "{{ test_items }}"

This error is not raised with any other Ansible version.