* @return the value with the specified row and column
   * @throws IndexOutOfBoundsException if either index is negative, {@code rowIndex} is greater than
   *     or equal to the number of allowed row keys, or {@code columnIndex} is greater than or equal
   *     to the number of allowed column keys
   */
  public @Nullable V at(int rowIndex, int columnIndex) {
    // In GWT array access never throws IndexOutOfBoundsException.

      }
    }
    return null;
  }

  /**
   * Determines whether two iterables contain equal elements in the same order. More specifically,
   * this method returns {@code true} if {@code iterable1} and {@code iterable2} contain the same
   * number of elements and every element of {@code iterable1} is equal to the corresponding element
   * of {@code iterable2}.
   */

   */
  Network<N, EndpointPair<N>> asNetwork();

  //
  // Element-level accessors
  //

  /**
   * Returns a live view of the edges in this graph whose endpoints include {@code node}.
   *
   * <p>This is equal to the union of incoming and outgoing edges.
   *
   * <p>If {@code node} is removed from the graph after this method is called, the {@code Set}
   * {@code view} returned by this method will be invalidated, and will throw {@code

    private final Iterator<Entry<E>> entryIterator;
    private @Nullable Entry<E> currentEntry;

    /** Count of subsequent elements equal to current element */
    private int laterCount;

    /** Count of all elements equal to current element */
    private int totalCount;

    private boolean canRemove;

    private final Iterator<Entry<E>> entryIterator;
    private @Nullable Entry<E> currentEntry;

    /** Count of subsequent elements equal to current element */
    private int laterCount;

    /** Count of all elements equal to current element */
    private int totalCount;

    private boolean canRemove;

constraints.Digits.message = {item} must be a number. (expected: <number>.<number>)
constraints.Future.message = {item} must be a future value.
constraints.Max.message = {item} must be less than or equal to {value}.
constraints.Min.message = {item} must be greater than or equal to {value}.
constraints.NotNull.message = {item} is required.
constraints.Null.message = {item} must be null.
constraints.Past.message = {item} must be a past value.

constraints.Digits.message = {item} must be a number. (expected: <number>.<number>)
constraints.Future.message = {item} must be a future value.
constraints.Max.message = {item} must be less than or equal to {value}.
constraints.Min.message = {item} must be greater than or equal to {value}.
constraints.NotNull.message = {item} is required.
constraints.Null.message = {item} must be null.
constraints.Past.message = {item} must be a past value.

/**
 * Tester for {@link Equivalence} relationships between groups of objects.
 *
 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
 * contains objects that are supposed to be equal to each other. Objects of different groups are
 * expected to be unequal. For example:
 *
 * {@snippet :
 * EquivalenceTester.of(someStringEquivalence)
 *     .addEquivalenceGroup("hello", "h" + "ello")

/**
 * Tester for {@link Equivalence} relationships between groups of objects.
 *
 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
 * contains objects that are supposed to be equal to each other. Objects of different groups are
 * expected to be unequal. For example:
 *
 * {@snippet :
 * EquivalenceTester.of(someStringEquivalence)
 *     .addEquivalenceGroup("hello", "h" + "ello")

  private static void assertMean(int expectedMean, int x, int y) {
    assertEquals(
        "The expectedMean should be the same as computeMeanSafely",
        expectedMean,
        computeMeanSafely(x, y));
    assertMean(x, y);
  }

  /**
   * Helper method that asserts the arithmetic mean of x and y is equal to the result of
   * computeMeanSafely.