class GroupStatistics { final double totalExpenses; final int expenseCount; final double averageExpense; final String topCategory; final Map categoryBreakdown; const GroupStatistics({ required this.totalExpenses, required this.expenseCount, required this.averageExpense, required this.topCategory, required this.categoryBreakdown, }); factory GroupStatistics.empty() { return const GroupStatistics( totalExpenses: 0.0, expenseCount: 0, averageExpense: 0.0, topCategory: '', categoryBreakdown: {}, ); } }