toJson method
Convert to JSON.
Implementation
@override
Map<String, dynamic> toJson() => {
...baseToJson(),
'columns': columns.map((c) => c.toJson()).toList(),
'rows': rows.map((r) => r.toJson()).toList(),
'headerRepeat': headerRepeat,
if (maxRows != null) 'maxRows': maxRows,
if (unit != null) 'unit': unit,
};