Describe where statement for null children

export type CategoryId = number & { __typeName: 'Category' };

export const categories = pgTable(
  'categories',
  {
    id: uuid('id').$type<ProductId>().defaultRandom().primaryKey(),
    createdAt: timestamp('createdAt').defaultNow().notNull(),
    title: varchar('title').notNull(),
    parentId: uuid('parent_id')
  },
)

export const categoriesRelations = relations(categories, ({ one, many }) => ({
  parent: one(categories, {
    fields: [categories.parentId],
    references: [categories.id],
  }),
  children: many(categories),
}))

drizzle.query.categories.findMany({
  where: (categories, { isNull }) => {
    // Property 'children' does not exist on type
    return isNull(categories.children)
  },
})