yml

What steps did you take:

Input:

#@ def group_alpha():
name: alpha
#@ end
groups: &all_groups
  - #@ group_alpha()
foo:
  groups: *all_groups

Result:

groups:
- null
foo:
  groups:
  - name: alpha

Expected:

groups:
- alpha
foo:
  groups:
  - name: alpha

Expected according to [limitations](https://carvel.dev/ytt/docs/latest/known-limitat

Similar to the Email validator.

Helm still doesn't support this functionality. helm/helm#6990
We can override this behavior with native helm pull and helm save to mktemp dir.