Using your example on the ticket, I added a "character varying (32)" column with NOT NULL to the table. When I then edit the column, and turn off NOT NULL (making no other changes), the SQL generated is:
ALTER TABLE public.test_drop
ALTER COLUMN col2 TYPE character varying (32) COLLATE pg_catalog."default";
ALTER TABLE public.test_drop
ALTER COLUMN col2 DROP NOT NULL;
I didn't see that when turning off NOT NULL for col1.