### Question:
MappingIterator implements Iterator<O> { @Override public boolean hasNext() { return input.hasNext(); } MappingIterator(Iterator<I> input, Function<I, O> mapper); @Override boolean hasNext(); @Override O next();  }### Answer:
@Test public void testInitializeWithoutIterator() { Iterator<String> iterator = new MappingIterator<>(null, String::valueOf); assertFalse(iterator.hasNext()); }