Can't alter column from `.notNull()` to `allow null`

Background

I have an SQLite db, and a schema.

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1').notNull(),
    // ...
  },
);

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1').notNull(),
    // ...
  },
);

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1').notNull(),
    // ...
  },
);

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1').notNull(),
    // ...
  },
);

I edited my schema to:

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1'),
    // ...
  },
);

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1'),
    // ...
  },
);

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1'),
    // ...
  },
);

// schema.ts
export const T1 = sqliteTable(
  'T1',
  {
    // ...
    C1: text('C1'),
    // ...
  },
);

Assuming the business logic is correct, I aimed to migrate my database with

drizzle-kit generate

drizzle-kit generate

drizzle-kit generate

drizzle-kit generate and <apply migration script>.

However, after running the generate script, no migration was generated. How can I make C1 allow

NULL

NULL

NULL

NULL values?

    "drizzle-kit": "^0.23.0",
    "drizzle-orm": "^0.31.0",

    "drizzle-kit": "^0.23.0",
    "drizzle-orm": "^0.31.0",

    "drizzle-kit": "^0.23.0",
    "drizzle-orm": "^0.31.0",

    "drizzle-kit": "^0.23.0",
    "drizzle-orm": "^0.31.0",

Related SEO tags so others can find the problem and the solution quicker: NOT NULL constraint failed