@Override
  public boolean isEmpty() {
    return sideInputs.isEmpty();
  }
@Test
  public void testIsEmptyTrue() {
    // Create an empty handler
    SideInputHandler emptySideInputHandler =
        new SideInputHandler(ImmutableList.of(), InMemoryStateInternals.<Void>forKey(null));
    assertTrue(emptySideInputHandler.isEmpty());
  }