Check if null in Polar

When you want to evaluate a JavaScript null inside Polar, you use nil instead of null. This is mentioned in the docs here.

Suppose you had a User class and Item class in JavaScript as follows:

class User {}

class Item {
  locked: boolean | null;
  constructor(props: { locked: boolean | null }) {
    this.locked = props.locked;
  }
}

It's pretty unrealistic to allow null for the locked property but this is for demonstration. From here, if you'd like to allow a read action when the locked property is null, you can write the polar policy as follows:

actor User {}

allow(actor, action, resource) if
  has_permission(actor, action, resource);

resource Item {
  permissions = ["read"];
}

has_permission(_actor: User, "read", item: Item) if
  item.locked = nil; # use `nil` to check `null`

See how nil is used to check if item.locked is null in the JavaScript side.

You can verify that this works as expected with the code bellow.

// Arrange
const user = new User();
const item = new Item({ locked: null });

// Act & Assert
await expect(oso.authorize(user, 'read', item)).resolves.toBeUndefined();