@Override
    @CheckForNull
    V getValue(int index) {
      return at(index, columnIndex);
    }

    @Override
    @CheckForNull
    V setValue(int index, @CheckForNull V newValue) {
      return set(index, columnIndex, newValue);
    }
  }

  /**
   * Returns an immutable set of the valid column keys, including those that are associated with
   * null values only.
   *

    @Override
    @CheckForNull
    V getValue(int index) {
      return at(index, columnIndex);
    }

    @Override
    @CheckForNull
    V setValue(int index, @CheckForNull V newValue) {
      return set(index, columnIndex, newValue);
    }
  }

  /**
   * Returns an immutable set of the valid column keys, including those that are associated with
   * null values only.
   *