Comment by zeugmasyllepsis

Playing around in a docker image of the beta build, it looks like this allows you to add a `unique nulls not distinct` constraint to a composite set of fields, but still does not allow you to specify those same fields a primary key. For example

    -- This works
    alter table announcement_destinations
        add constraint announcement_destinations_pk unique nulls not distinct (sender, receiving_group, optional_filter);

but

    -- Still does not work
    alter table announcement_destinations
        add constraint announcement_destinations_pk2 primary key (sender, receiving_group, optional_filter);

fails with a message like "ERROR: column "optional_filter" of relation "announcement_destinations" contains null values". Is there a motivation for this distinction?