'dict object' has no attribute 'datasource'

Hello,
On a fresh installation, I have the following error

TASK [ceph-grafana : Set grafana_data_source] ***************************************************************************************************************************************************************
task path: /usr/share/cephmetrics-ansible/roles/ceph-grafana/tasks/configure_grafana.yml:51
fatal: [dell-per320-04.rhts.gsslab.pek.redhat.com]: FAILED! => {
"failed": true,
"msg": "The task includes an option with an undefined variable. The error was: 'dict object' has no attribute 'datasource'\n\nThe error appears to have been in '/usr/share/cephmetrics-ansible/roles/ceph-grafana/tasks/configure_grafana.yml': line 51, column 3, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n\n- name: Set grafana_data_source\n ^ here\n\nexception type: \nexception: 'dict object' has no attribute 'datasource'"
}

Just added host in [ceph-grafana] from /etc/ansible/hosts, created vars.yml to pass admin password and issue the command under /usr/share/cephmetrics-ansible.
ansible-playbook -v playbook.yml -e '@vars.yml'