* and allowing callers to pass arguments that a nullness checker believes could be null.
   *
   * We still encourage people to use requireNonNull over checkNotNull for non-precondition checks.
   */

  /**
   * Ensures that an object reference passed as a parameter to the calling method is not null.
   *
   * @param reference an object reference

        assertEquals("PASSED", pom.getValue(prefix + "propertiesFile"));
        assertEquals("PASSED", pom.getValue(prefix + "parent"));
        assertEquals("PASSED-1", pom.getValue(prefix + "stringParams/stringParam[1]"));
        assertEquals("PASSED-3", pom.getValue(prefix + "stringParams/stringParam[2]"));
        assertEquals("PASSED-2", pom.getValue(prefix + "stringParams/stringParam[3]"));

   * and allowing callers to pass arguments that a nullness checker believes could be null.
   *
   * We still encourage people to use requireNonNull over checkNotNull for non-precondition checks.
   */

  /**
   * Ensures that an object reference passed as a parameter to the calling method is not null.
   *
   * @param reference an object reference

   * IllegalArgumentException} if passed a {@code fromKey} less than an earlier {@code fromKey}.
   * However, this method doesn't throw an exception in that situation, but instead keeps the
   * original {@code fromKey}. Similarly, this method keeps the original {@code toKey}, instead of
   * throwing an exception, if passed a {@code toKey} greater than an earlier {@code toKey}.
   */
  @Override

   * IllegalArgumentException} if passed a {@code fromKey} less than an earlier {@code fromKey}.
   * However, this method doesn't throw an exception in that situation, but instead keeps the
   * original {@code fromKey}. Similarly, this method keeps the original {@code toKey}, instead of
   * throwing an exception, if passed a {@code toKey} greater than an earlier {@code toKey}.
   */
  @Override

     *
     * <p>Canceling this future will attempt to cancel all the component futures.
     *
     * @return a future whose result is based on {@code combiner} (or based on the input futures
     *     passed to {@code whenAllSucceed}, if that is the method you used to create this {@code
     *     FutureCombiner}). Even if you don't care about the value of the future, you should

   * the two sets. If you have reason to believe one of your sets will generally be smaller than the
   * other, pass it first. Unfortunately, since this method sets the generic type of the returned
   * set based on the type of the first set passed, this could in rare cases force you to make a
   * cast, for example:
   *
   * <pre>{@code
   * Set<Object> aFewBadObjects = ...

   * @Nullable X>, then users might pass a TypeParameter<Y>, where Y is a subtype of X, while still
   * passing a TypeToken<X>. This would be invalid. Maybe we could accept a TypeParameter<@PolyNull
   * X> if we support such a thing? It would be weird or misleading for users to be able to pass
   * `new TypeParameter<@Nullable T>() {}` and have it act as a plain `TypeParameter<T>`, but

    assertEquals("c", itr2.next());
    assertEquals("d", itr2.next());
  }

  /** Illustrates the somewhat bizarre behavior when a null is passed in. */
  public void testConcatContainingNull() {
    Iterator<Iterator<Integer>> input =
        (Iterator<Iterator<Integer>>)
            Arrays.<@Nullable Iterator<Integer>>asList(iterateOver(1, 2), null, iterateOver(3))

/**
 * Synchronized collection views. The returned synchronized collection views are serializable if the
 * backing collection and the mutex are serializable.
 *
 * <p>If {@code null} is passed as the {@code mutex} parameter to any of this class's top-level
 * methods or inner class constructors, the created object uses itself as the synchronization mutex.
 *
 * <p>This class should be used by other collection classes only.