null error on adding split data saved in the controller.

[RJ2607]

E/flutter (25295): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'Null' is not a subtype of type 'String'
E/flutter (25295): #0 new DailySpendingModel.fromJson (package:paysa/Models/DailySpendingModel.dart:32:15)
E/flutter (25295): #1 _DailySpendingScreenState._fetchData (package:paysa/Views/DailySpendings/DailySpending.dart:91:41)
E/flutter (25295):
E/flutter (25295):