code: public GridCell<P> createCellAt(int row, int column) {
  		GridCell<P> cell = this.cells[row][column];
  		if (cell == null) {
  			cell = new GridCell<>(row, column, getCellBounds(row, column));
  			this.cells[row][column] = cell;
  			++this.cellCount;
  		}
  		return cell;
  	}
docs: Create a cell at the specified location if there is no
  cell at this location.
  
  @param row the row index.
  @param column the column index.
  @return the cell.