Use .toBeNil when checking a value is null or undefined

import {
  defineExpect,
  not,
  test,
  toBeNil,
} from "https://deno.land/x/unitest@$VERSION/mod.ts";

const expect = defineExpect({
  matcherMap: {
    toBeNil,
  },
  modifierMap: {
    not,
  },
});

test("passes when value is null or undefined", () => {
  expect(null).toBeNil();
  expect(undefined).toBeNil();
  expect(true).not.toBeNil();
});