DEPRECATION WARNING with mariadb_tls_files on ansible version 2.12

[roumano]

Describe the bug
If we set mariadb_tls_files variables,these tasks will be executed :

• setup_cluster | create TLS certificates directory
• setup_cluster | copy TLS CA cert, server cert & private key

The when condition on them are badly written and we receive a DEPRECATION WARNING on them :

TASK [ansible-mariadb-galera-cluster : setup_cluster | create TLS certificates directory] ****************************************************************************************************
[DEPRECATION WARNING]: evaluating 'mariadb_tls_files' as a bare variable, this behaviour will go away and you might need to add |bool to the expression in the future. Also see 
CONDITIONAL_BARE_VARS configuration toggle. This feature will be removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.

TASK [ansible-mariadb-galera-cluster : setup_cluster | copy TLS CA cert, server cert & private key] ******************************************************************************************
[DEPRECATION WARNING]: evaluating 'mariadb_tls_files' as a bare variable, this behaviour will go away and you might need to add |bool to the expression in the future. Also see 
CONDITIONAL_BARE_VARS configuration toggle. This feature will be removed in version 2.12. Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.

To Reproduce
Steps to reproduce the behaviour:

1. Set the variable mariadb_tls_files
   like in my example :

mariadb_tls_files:
  ca_cert:
    name: "ca.pem"
    content: "{{ lookup('file', 'files/STAR..ca') }}"
  server_key:
    name: "server-key.pem"
    content: "{{ lookup('file', 'STAR.key') }}"
  server_cert:
    name: "server-cert.pem"
    content: "{{ lookup('file', 'files/STAR.crt') }}"

2. run the playbook
3. See the warning

Expected behavior
A clear and concise description of what you expected to happen.
A better when condution on these tasks