Foreign keys default to NOT NULL with PostgreSQL

export const assetTable = pgTable(
    'asset',
    {
        id: serial('id').primaryKey(),
    },
);

export const trackTable = pgTable(
    'track',
    {
        id: serial('id').primaryKey(),
        // TODO: investigate why foreign keys default to NOT NULL
        originalAssetId: serial('original_asset_id').references(
            () => assetTable.id,
            {
                onDelete: 'cascade',
            },
        ),
    },
);

CREATE TABLE IF NOT EXISTS "asset" (
    "id" serial PRIMARY KEY NOT NULL,
);

CREATE TABLE IF NOT EXISTS "track" (
    "id" serial PRIMARY KEY NOT NULL,
    "original_asset_id" serial NOT NULL,
);