it("deepKeys should not cause an error with sparsed arrays", () => {
  // fixture setup
  const mockedEntity = {
    // eslint-disable-next-line no-sparse-arrays
    open_hours: [1, , 3],
  };

  const sut = () => {
    deepKeys(mockedEntity);
  };

  // exercise system
  // verify outcome
  expect(sut).not.toThrow();
});