TableCollectors.toImmutableTable(Cell::getRowKey, Cell::getColumnKey, t -> null);
    try {
      Stream.of(immutableCell("one", "uno", 1)).collect(collector);
      fail("Expected NullPointerException");
    } catch (NullPointerException expected) {
    }
    collector =
        TableCollectors.toImmutableTable(Cell::getRowKey, Cell::getColumnKey, Cell::getValue);
    try {

  }

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

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

          (Cell<R, C, V> cell1, Cell<R, C, V> cell2) -> {
            int rowCompare =
                (rowComparator == null)
                    ? 0
                    : rowComparator.compare(cell1.getRowKey(), cell2.getRowKey());
            if (rowCompare != 0) {
              return rowCompare;
            }
            return (columnComparator == null)
                ? 0

                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> {

                      @SuppressWarnings("unchecked")
                      Cell<String, Integer, Character> cell =
                          (Cell<String, Integer, Character>) element;
                      table.put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
                    }
                    return table.cellSet();
                  }

                  @Override

                      @SuppressWarnings("unchecked")
                      Cell<String, Integer, Character> cell =
                          (Cell<String, Integer, Character>) element;
                      table.put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
                    }
                    return table.cellSet();
                  }

                  @Override

  }

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

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

        Cell<?, ?, ?> other = (Cell<?, ?, ?>) obj;
        return Objects.equal(getRowKey(), other.getRowKey())
            && Objects.equal(getColumnKey(), other.getColumnKey())
            && Objects.equal(getValue(), other.getValue());
      }
      return false;
    }

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

    @Override

    this.singleRowKey = checkNotNull(rowKey);
    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)

        checkNotNull(cell.getRowKey(), "row");
        checkNotNull(cell.getColumnKey(), "column");
        checkNotNull(cell.getValue(), "value");
        @SuppressWarnings("unchecked") // all supported methods are covariant
        Cell<R, C, V> immutableCell = (Cell<R, C, V>) cell;
        cells.add(immutableCell);
      } else {
        put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
      }