collector = toImmutableTable(Cell::getRowKey, Cell::getColumnKey, t -> null);
      assertThrows(
          NullPointerException.class,
          () -> Stream.of(immutableCell("one", "uno", 1)).collect(collector));
    }
    {
      Collector<Cell<String, String, Integer>, ?, ImmutableTable<String, String, Integer>>
          collector = toImmutableTable(Cell::getRowKey, Cell::getColumnKey, Cell::getValue);
      assertThrows(

  }

  @Override
  public void putAll(Table<? extends R, ? extends C, ? extends V> table) {
    for (Table.Cell<? extends R, ? extends C, ? extends V> cell : table.cellSet()) {
      put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
    }
  }

  @LazyInit private transient @Nullable Set<Cell<R, C, V>> cellSet;

  @Override
  public Set<Cell<R, C, V>> cellSet() {
    Set<Cell<R, C, V>> result = cellSet;

                mergeFunction),
        (table1, table2) -> {
          for (Table.Cell<R, C, V> cell2 : table2.cellSet()) {
            mergeTables(
                table1, cell2.getRowKey(), cell2.getColumnKey(), cell2.getValue(), mergeFunction);
          }
          return table1;
        });
  }

  private static final class ImmutableTableCollectorState<R, C, V> {

            if (rowCompare != 0) {
              return rowCompare;
            }
            return (columnComparator == null)
                ? 0
                : columnComparator.compare(cell1.getColumnKey(), cell2.getColumnKey());
          };
      sort(cells, comparator);
    }
    return forCellsInternal(cells, rowComparator, columnComparator);
  }

  }

  @Override
  public void putAll(Table<? extends R, ? extends C, ? extends V> table) {
    for (Table.Cell<? extends R, ? extends C, ? extends V> cell : table.cellSet()) {
      put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
    }
  }

  @LazyInit private transient @Nullable Set<Cell<R, C, V>> cellSet;

  @Override
  public Set<Cell<R, C, V>> cellSet() {
    Set<Cell<R, C, V>> result = cellSet;

        return Objects.equals(getRowKey(), other.getRowKey())
            && Objects.equals(getColumnKey(), other.getColumnKey())
            && Objects.equals(getValue(), other.getValue());
      }
      return false;
    }

    @Override
    public int hashCode() {
      return Objects.hash(getRowKey(), getColumnKey(), getValue());
    }

    @Override
    public String toString() {

                      @SuppressWarnings("unchecked")
                      Cell<String, Integer, Character> cell =
                          (Cell<String, Integer, Character>) element;
                      columnKeys.add(cell.getColumnKey());
                    }
                    Table<String, Integer, Character> table =
                        ArrayTable.create(ImmutableList.of("bar"), columnKeys);
                    for (Object element : elements) {

                mergeFunction),
        (table1, table2) -> {
          for (Table.Cell<R, C, V> cell2 : table2.cellSet()) {
            mergeTables(
                table1, cell2.getRowKey(), cell2.getColumnKey(), cell2.getValue(), mergeFunction);
          }
          return table1;
        });
  }

  private static final class ImmutableTableCollectorState<R, C, V> {

    int[] cellColumnInRowIndices = new int[cellList.size()];
    for (int i = 0; i < cellList.size(); i++) {
      Cell<R, C, V> cell = cellList.get(i);
      R rowKey = cell.getRowKey();
      C columnKey = cell.getColumnKey();
      V value = cell.getValue();

      /*
       * These requireNonNull calls are safe because we construct the maps to hold all the provided
       * cells.
       */

    this.singleColumnKey = checkNotNull(columnKey);
    this.singleValue = checkNotNull(value);
  }

  SingletonImmutableTable(Cell<R, C, V> cell) {
    this(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
  }

  @Override
  public ImmutableMap<R, V> column(C columnKey) {
    checkNotNull(columnKey);
    return containsColumn(columnKey)
        ? ImmutableMap.of(singleRowKey, singleValue)