cell() {
        return new ArgHandler('Sheet.cell')
            .case('string', address => {
                const ref = addressConverter.fromAddress(address);
                if (ref.type !== 'cell') throw new Error('Sheet.cell: Invalid address.');
                return this.row(ref.rowNumber).cell(ref.columnNumber);
            })
            .case(['number', '*'], (rowNumber, columnNameOrNumber) => {
                return this.row(rowNumber).cell(columnNameOrNumber);
            })
            .handle(arguments);
    }
Gets the cell with the given row and column numbers.
@param {number} rowNumber - The row number of the cell.
@param {string|number} columnNameOrNumber - The column name or number of the cell.
@returns {Cell} The cell.