}
    this.cellRowIndices = cellRowIndices;
    this.cellColumnIndices = cellColumnIndices;
    this.rowMap = new RowMap();
    this.columnMap = new ColumnMap();
  }

  /** An immutable map implementation backed by an indexed nullable array. */
  private abstract static class ImmutableArrayMap<K, V> extends IteratorBasedImmutableMap<K, V> {
    private final int size;

    ImmutableArrayMap(int size) {
      this.size = size;

    }
    this.cellRowIndices = cellRowIndices;
    this.cellColumnIndices = cellColumnIndices;
    this.rowMap = new RowMap();
    this.columnMap = new ColumnMap();
  }

  /** An immutable map implementation backed by an indexed nullable array. */
  private abstract static class ImmutableArrayMap<K, V> extends IteratorBasedImmutableMap<K, V> {
    private final int size;

    ImmutableArrayMap(int size) {
      this.size = size;