<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below -->

##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->

postgresql_slot, postgresql_user

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.3
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['~/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python3.7/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 3.7.4 (default, Jul 16 2019, 07:12:58) [GCC 9.1.0]
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->
archlinux latest

##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml
- postgresql_user:
    name: user1
    password: password
  become: true
  become_user: postgres

- postgresql_slot:
    name: slot1
  become: true
  become_user: postgres
```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->
Consistent warnings. Either both postgresql_user and postgresql_slot should give a warning or neither should.

##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->
postgresql_slot gives warning "[WARNING]: Database name has not been passed, used default database to connect to." but postgresql_user doesn't, even though both of them have not specified a database.
return exec_sql(self, "SELECT 1 FROM pg_roles WHERE rolname = '%s'" % role, add_to_executed=False)
#
def main():
    argument_spec = postgres_common_argument_spec()
    argument_spec.update(
        groups=dict(type='list', aliases=['group', 'source_role', 'source_roles']),
        target_roles=dict(type='list', aliases=['target_role', 'user', 'users']),
        fail_on_role=dict(type='bool', default=True),
        state=dict(type='str', default='present', choices=['absent', 'present']),
        db=dict(type='str', aliases=['login_db']),
        session_role=dict(type='str'),
    )
    module = AnsibleModule(
        argument_spec=argument_spec,
        supports_check_mode=True,
    )
    groups = module.params['groups']
    target_roles = module.params['target_roles']
    fail_on_role = module.params['fail_on_role']
    state = module.params['state']
    conn_params = get_conn_params(module, module.params)
    db_connection = connect_to_db(module, conn_params, autocommit=False)
    cursor = db_connection.cursor(cursor_factory=DictCursor)