transform(not_null={"col": False}) adds NOT NULL to a nullable column #944

transform() only removes a column from the NOT NULL set if it's already there. Otherwise False falls into the else branch and adds it:

db["dogs"].insert({"id": 1, "name": "Cleo", "age": None}, pk="id")
db["dogs"].transform(not_null={"age": False})
# sqlite3.IntegrityError: NOT NULL constraint failed: dogs_new_....age

If the column has no nulls yet, it silently becomes NOT NULL. The CLI does the same:

sqlite-utils transform b.db dogs --not-null-false age

gives "age" INTEGER NOT NULL.