int[] cellColumnIndices = new int[cellSet().size()];
    int i = 0;
    for (Cell<R, C, V> cell : cellSet()) {
      // requireNonNull is safe because the cell exists in the table.
      cellColumnIndices[i++] = requireNonNull(columnKeyToIndex.get(cell.getColumnKey()));
    }
    return SerializedForm.create(this, cellRowIndices, cellColumnIndices);
  }

      values[rowIndex][columnIndex] = cell.getValue();
      rowCounts[rowIndex]++;
      columnCounts[columnIndex]++;
      cellRowIndices[i] = rowIndex;
      cellColumnIndices[i] = columnIndex;
    }
    this.cellRowIndices = cellRowIndices;
    this.cellColumnIndices = cellColumnIndices;
    this.rowMap = new RowMap();
    this.columnMap = new ColumnMap();
  }

  /** An immutable map implementation backed by an indexed nullable array. */

    int[] cellColumnIndices = new int[cellSet().size()];
    int i = 0;
    for (Cell<R, C, V> cell : cellSet()) {
      // requireNonNull is safe because the cell exists in the table.
      cellColumnIndices[i++] = requireNonNull(columnKeyToIndex.get(cell.getColumnKey()));
    }
    return SerializedForm.create(this, cellRowIndices, cellColumnIndices);
  }