code: ImmutableCell<V> validateCounts(int rowCount, int columnCount) {
          if (row >= rowCount || column >= columnCount) {
              throw new IndexOutOfBoundsException("Invalid row-column: " + row + "," + column + " for grid " + rowCount + "x" + columnCount);
          }
          return this;
      }
docs: Validates this cell against the specified counts.