The below task is not working as expected.
i am expecting it will print message for at least 2 times which is defined and skip rest 2.
TASK [Connect to Isilon Device] ****************************************************************************************************
skipping: [localhost]
I believe the loop: values are evaluated first, before any iterations are performed, in which case any undefined variables in any of the loop: expressions will throw the error you see.
This is probably a desirable behavior in general even though in this case you got caught by surprise.
Here’s a work-around that uses a sentinel value — and blatantly abuses “omit” for which I’m sure to be rightly scorned. 
**---** **- name: "Loop Iteration List"** **hosts: localhost** **vars:** **nfs_prod_target_id: "Khan"** **nfs_prod_source_id: "Siddque"** **tasks:** **- name: "Connect to Isilon Device"** **ansible.builtin.debug:** **msg: "{{ item }}"** **when: item != omit** **loop:** **- "{{ nfs_prod_source_id | d(omit) }}"** **- "{{ nfs_prod_target_id | d(omit) }}"** **- "{{ nfs_dev_source_id | d(omit) }}"** **- "{{ nfs_dev_target_id | d(omit) }}"**
Cheers,
Just wonder what’s stopping you from doing this: