You may observe that any list has at least one permutation. The empty list's only permutation is the empty list itself, so:

λ Relude.List.permutations [ ]
[[]]

This behaviour is also theoretically sound since permutations of a list are a model of a symmetric group and a group always has at least one element.

It is nicer to have to drop from a NonEmpty to a list than to lift from a list to NonEmpty, since the latter requires the handling of the spurious case of the list being empty.