if (oldCell == null) {
        MutableCell<R, C, V> cell = new MutableCell<>(row, column, value);
        insertionOrder.add(cell);
        table.put(row, column, cell);
      } else {
        oldCell.merge(value, merger);
      }
    }

    ImmutableTableCollectorState<R, C, V> combine(
        ImmutableTableCollectorState<R, C, V> other, BinaryOperator<V> merger) {

   *
   * @throws UnsupportedOperationException always
   * @deprecated Unsupported operation.
   */
  @Deprecated
  @Override
  @DoNotCall("Always throws UnsupportedOperationException")
  public final void merge(
      Range<K> range,
      @CheckForNull V value,
      BiFunction<? super V, ? super @Nullable V, ? extends @Nullable V> remappingFunction) {
    throw new UnsupportedOperationException();
  }

  @Override

            immutableCell("two", "dos", 2),
            immutableCell("three", "tres", 3));
  }

  public void testToTableNullMerge() {
    // TODO github.com/google/guava/issues/6824 - the null merge feature is not compatible with the
    // current nullness annotation of the mergeFunction parameter. Work around with casts.
    BinaryOperator<@Nullable Integer> mergeFunction = (v1, v2) -> null;

    }
    try {
      unmod.compute(4, (k, v) -> v);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      unmod.merge(4, "four", (k, v) -> v);
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      unmod.clear();

    checkNotNull(iterators, "iterators");
    checkNotNull(comparator, "comparator");

    return new MergingIterator<>(iterators, comparator);
  }

  /**
   * An iterator that performs a lazy N-way merge, calculating the next value each time the iterator
   * is polled. This amortizes the sorting cost over the iteration and requires less memory than
   * sorting all elements at once.
   *