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());

  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");