Enumeration<Integer> enumer = Iterators.asEnumeration(iter);

    assertFalse(enumer.hasMoreElements());
    assertThrows(NoSuchElementException.class, () -> enumer.nextElement());
  }

  public void testAsEnumerationSingleton() {
    Iterator<Integer> iter = ImmutableList.of(1).iterator();
    Enumeration<Integer> enumer = Iterators.asEnumeration(iter);

    assertTrue(enumer.hasMoreElements());

    Enumeration<Integer> enumer = Iterators.asEnumeration(iter);

    assertFalse(enumer.hasMoreElements());
    assertThrows(NoSuchElementException.class, () -> enumer.nextElement());
  }

  public void testAsEnumerationSingleton() {
    Iterator<Integer> iter = ImmutableList.of(1).iterator();
    Enumeration<Integer> enumer = Iterators.asEnumeration(iter);

    assertTrue(enumer.hasMoreElements());

   * you have a {@link Collection}), or {@code Iterators.asEnumeration(collection.iterator())}.
   */
  // This is an adapter for cases in which users do need an Enumeration for whatever reason.
  @SuppressWarnings("JdkObsolete")
  public static <T extends @Nullable Object> Enumeration<T> asEnumeration(Iterator<T> iterator) {
    checkNotNull(iterator);
    return new Enumeration<T>() {

   * you have a {@link Collection}), or {@code Iterators.asEnumeration(collection.iterator())}.
   */
  // This is an adapter for cases in which users do need an Enumeration for whatever reason.
  @SuppressWarnings("JdkObsolete")
  public static <T extends @Nullable Object> Enumeration<T> asEnumeration(Iterator<T> iterator) {
    checkNotNull(iterator);
    return new Enumeration<T>() {

  public void testFromPropertiesNullKey() {
    Properties properties =
        new Properties() {
          @Override
          public Enumeration<?> propertyNames() {
            return Iterators.asEnumeration(asList(null, "first", "second").iterator());
          }
        };
    properties.setProperty("first", "true");
    properties.setProperty("second", "null");