Ansible: Run a task only when variable is not empty

Question

I have following play book:

test2.yml:

- hosts: localhost
  connection: local
  gather_facts: false

  vars:
    dict1:
      v1:
        - 111
        - 222
        - 333
      v2:

    ver: "{{ ver }}"

  tasks:
    - name: Gather list
      set_fact: rblist="{{ pitem }}"
      with_dict: "{{ dict1 }}"
      when: "pitem.key in ver"
      loop_control:
       loop_var: pitem
      register: plist

    - name: lets include the task if the value is not empty
      include: test3.yml
      when: rblist.value

test3.yml:

---
  - name: display value if not empty
    debug: msg={{ rblist.value }}

I'd like to invoke test3.yml only when rblist.value is not empty, but its ignoring that and invokes the task even when the value is empty.

When the value is not empty: it works fine

ansible-playbook test2.yml -e "ver=v1"

PLAY [localhost] ************************************************************************************************************************************************************************************************************************

TASK [Gather list] **********************************************************************************************************************************************************************************************************************
ok: [localhost] => (item={u'key': u'v1', u'value': [111, 222, 333]})

TASK [display value if not empty] *******************************************************************************************************************************************************************************************************
ok: [localhost] => {
    "msg": [
        111, 
        222, 
        333
    ]
}

PLAY RECAP ******************************************************************************************************************************************************************************************************************************
localhost                  : ok=2    changed=0    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

When the value is empty: seems to behave same as when the list

ansible-playbook test2.yml -e "ver=v2"

PLAY [localhost] ************************************************************************************************************************************************************************************************************************

TASK [Gather list] **********************************************************************************************************************************************************************************************************************
ok: [localhost] => (item={u'key': u'v2', u'value': None})

TASK [display value if not empty] *******************************************************************************************************************************************************************************************************

PLAY RECAP ******************************************************************************************************************************************************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0   

Following How to test that a registered variable is not empty? and other solutions, I have tried the following

when: rblist.value | length > 0

I get this:

TASK [display value if not empty] *******************************************************************************************************************************************************************************************************
fatal: [localhost]: FAILED! => {"msg": "The conditional check 'rblist.value | length > 0' failed. The error was: Unexpected templating type error occurred on ({% if rblist.value | length > 0 %} True {% else %} False {% endif %}): object of type 'NoneType' has no len()\n\nThe error appears to be in '/stage/ap/ansible/test/test3.yml': line 2, column 5, but may\nbe elsewhere in the file depending on the exact syntax problem.\n\nThe offending line appears to be:\n\n---\n  - name: display value if not empty\n    ^ here\n"}

When I try this:

when: rblist.value != None

I get this:

ansible-playbook test2.yml -e "ver=v2"

PLAY [localhost] ************************************************************************************************************************************************************************************************************************

TASK [Gather list] **********************************************************************************************************************************************************************************************************************
ok: [localhost] => (item={u'key': u'v2', u'value': None})

TASK [display value if not empty] *******************************************************************************************************************************************************************************************************

PLAY RECAP ******************************************************************************************************************************************************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0   

I Tried this:

when: rblist.value != ""

Same results as above that is when used != None

Answer 1

You probably have

display_skipped_hosts = false

in your ansible.cfg file.

Where display_skipped_hosts:

Toggle to control displaying skipped task/host entries in a task in the default callback

^{Source: https://docs.ansible.com/ansible/2.9/reference_appendices/config.html#display-skipped-hosts}

With this option set this way, you will not see skipped host in the play itself, but you can see them in your recap:

PLAY RECAP ********************************************************************************************************
localhost                  : ok=1    changed=0    unreachable=0    failed=0    skipped=1    rescued=0    ignored=0 

Where the important part is skipped=1.

You will thus still see the task description, but nothing under it, confirming that the task was skipped.