Help to accept empty block or block with only valid list entries

[rfuehrer]

I would like to check a user-maintained YAML in which a "subscription" block can be included. This should contain list entries. If this block exists, but is specified without subitems/list elements, it should be accepted. If a list element is specified, it must exist as a string.

Permitted:

before:
   - ok1
   - ok2

subscription:

after:
  - ok1
  - ok2

or

before:
   - ok1
   - ok2

subscription:
  - test1
  - test2

after:
  - ok1
  - ok2

Not allowed:

before:
   - ok1
   - ok2

subscription:
  -

after:
  - ok1
  - ok2

Can this be implemented with Yamale?

[nbaju1]

This schema should do what you want.

before: list(str())
subscription: list(str(), required=False, nullable=True)
after: list(str())