/**
   * @throws IllegalArgumentException if {@code existingValue} is not null.
   */
  /*
   * We could have declared this method 'static' but the additional compile-time checks achieved by
   * referencing the type variables seem worthwhile.
   */
  final void checkNoDuplicate(R rowKey, C columnKey, @Nullable V existingValue, V newValue) {
    checkArgument(
        existingValue == null,

  /**
   * @throws IllegalArgumentException if {@code existingValue} is not null.
   */
  /*
   * We could have declared this method 'static' but the additional compile-time checks achieved by
   * referencing the type variables seem worthwhile.
   */
  final void checkNoDuplicate(R rowKey, C columnKey, @Nullable V existingValue, V newValue) {
    checkArgument(
        existingValue == null,

      int rowIndex = requireNonNull(rowKeyToIndex.get(rowKey));
      int columnIndex = requireNonNull(columnKeyToIndex.get(columnKey));
      V existingValue = values[rowIndex][columnIndex];
      checkNoDuplicate(rowKey, columnKey, existingValue, cell.getValue());
      values[rowIndex][columnIndex] = cell.getValue();
      rowCounts[rowIndex]++;
      columnCounts[columnIndex]++;
      cellRowIndices[i] = rowIndex;

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "putIfAbsent(present, existingValue) should return present or throw",
          v0(),
          putIfAbsent(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

      int rowIndex = requireNonNull(rowKeyToIndex.get(rowKey));
      int columnIndex = requireNonNull(columnKeyToIndex.get(columnKey));
      V existingValue = values[rowIndex][columnIndex];
      checkNoDuplicate(rowKey, columnKey, existingValue, cell.getValue());
      values[rowIndex][columnIndex] = cell.getValue();
      rowCounts[rowIndex]++;
      columnCounts[columnIndex]++;
      cellRowIndices[i] = rowIndex;

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "putIfAbsent(present, existingValue) should return present or throw",
          v0(),
          getMap().putIfAbsent(k0(), v0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "putIfAbsent(present, existingValue) should return present or throw",
          v0(),
          putIfAbsent(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "putIfAbsent(present, existingValue) should return present or throw",
          v0(),
          getMap().putIfAbsent(k0(), v0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  }

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPut_unsupportedPresentExistingValue() {
    try {
      assertEquals("put(present, existingValue) should return present or throw", v0(), put(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)

  }

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPut_unsupportedPresentExistingValue() {
    try {
      assertEquals("put(present, existingValue) should return present or throw", v0(), put(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)