categories top-level property Null safety

Implementation

FruitCategory categories = FruitCategory(
  const Fruit('fruit'),
  <FruitCategory>{
    FruitCategory(
      const Fruit('apple'),
      <FruitCategory>{
        FruitCategory(
          const Fruit('red'),
          <FruitCategory>[
            FruitCategory(const Fruit('Red Delicious')),
            FruitCategory(const Fruit('Fuji')),
            FruitCategory(const Fruit('Crispin')),
            FruitCategory(const Fruit('Pink Lady')),
          ],
        ),
        FruitCategory(
          const Fruit('yellow'),
          <FruitCategory>[
            FruitCategory(const Fruit('Yellow Delicious')),
            FruitCategory(const Fruit('Ginger Gold')),
          ],
        ),
        FruitCategory(
          const Fruit('green'),
          <FruitCategory>[
            FruitCategory(const Fruit('Granny Smith')),
          ],
        ),
      },
    ),
    FruitCategory(
      const Fruit('berry'),
      <FruitCategory>{
        FruitCategory(const Fruit('blueberry')),
        FruitCategory(const Fruit('raspberry')),
      },
    ),
  },
);