nonNullCollections flag isn't being respected for alias types

[a-k-g]

What happened?

We have the following conjure type:

  AndSearchFilter:
    docs: |
      A SearchFilter used to combine multiple SearchFilters.
      A row satisfies this SearchFilter if and only if it satisfies all combined SearchFilters.
    alias: set<SearchFilter>

And we have enabled the nonNullCollections flag to enforce that the set cannot contain null entries. However, this is not being enforced.

What did you want to happen?

Constructing the AndSearchFilter with a set containing null should fail.