* @return the non-null reference that was validated
   * @throws NullPointerException if {@code reference} is null
   * @see Verify#verifyNotNull Verify.verifyNotNull()
   */
  @CanIgnoreReturnValue
  public static <T> T checkNotNull(@CheckForNull T reference) {
    if (reference == null) {
      throw new NullPointerException();
    }
    return reference;
  }

  /**

   * comparable.
   *
   * @throws ClassCastException if the keys in {@code map} are not mutually comparable
   * @throws NullPointerException if any key or value in {@code map} is null
   * @throws IllegalArgumentException if any two keys are equal according to their natural ordering
   */

   * comparable.
   *
   * @throws ClassCastException if the keys in {@code map} are not mutually comparable
   * @throws NullPointerException if any key or value in {@code map} is null
   * @throws IllegalArgumentException if any two keys are equal according to their natural ordering
   */

   * set is serializable.
   *
   * @param elements the elements that the set should contain
   * @return a new thread-safe set containing those elements (minus duplicates)
   * @throws NullPointerException if {@code elements} or any of its contents is null
   * @since 15.0
   */
  public static <E> Set<E> newConcurrentHashSet(Iterable<? extends E> elements) {
    Set<E> set = newConcurrentHashSet();

      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testToMapWithNullValues() {
    Iterable<String> strings = ImmutableList.of("one", "two", "three");
    try {
      Maps.toMap(strings, Functions.constant(null));
      fail();
    } catch (NullPointerException expected) {
    }
  }

      fail();
    } catch (NullPointerException expected) {
    }
  }

  public void testToMapWithNullValues() {
    Iterable<String> strings = ImmutableList.of("one", "two", "three");
    try {
      Maps.toMap(strings, Functions.constant(null));
      fail();
    } catch (NullPointerException expected) {
    }
  }

    assertEquals(2, (int) result.next());
    try {
      result.hasNext();
      fail("no exception thrown");
    } catch (NullPointerException e) {
    }
    try {
      result.next();
      fail("no exception thrown");
    } catch (NullPointerException e) {
    }
    // There is no way to get "through" to the 3.  Buh-bye
  }

  public void testConcatVarArgsContainingNull() {
    try {

   * necessary.
   *
   * <p>The returned iterator supports {@code remove()} when the corresponding input iterator
   * supports it.
   *
   * @throws NullPointerException if any of the provided iterators is null
   */
  @SafeVarargs
  public static <T extends @Nullable Object> Iterator<T> concat(Iterator<? extends T>... inputs) {

    assertEquals(2, (int) result.next());
    try {
      result.hasNext();
      fail("no exception thrown");
    } catch (NullPointerException e) {
    }
    try {
      result.next();
      fail("no exception thrown");
    } catch (NullPointerException e) {
    }
    // There is no way to get "through" to the 3.  Buh-bye
  }

  public void testConcatVarArgsContainingNull() {
    try {

        final ModelResolver modelResolver = getModelResolver(request);
        if (workspaceResolver == null && modelResolver == null) {
            throw new NullPointerException(String.format(
                    "request.workspaceModelResolver and request.modelResolver cannot be null (parent POM %s and POM %s)",