I have a conditional for Hosts but it's not picking up 'localhost' as the default value. Can you please help?

---
- hosts: "{{ pod + '_SE_Cluster_' + cl | default(localhost) }}"

'pod' and 'cl' are 2 Variables that are passed and works fine when passed. The issue is only the localhost.

Output:

[WARNING]: Could not match supplied host pattern, ignoring: RDG1_SE_Cluster_1

I did not pass pod_SE_CLUSTER_cl and it should pickup localhost by default but it didn't as u can see above