anchor.diff:    List<TaskNote> tasknotes = [];
     DateTime scheduled;
     int timestamp;
  -  Set<String> taskcategories = new Set();
  +  Set<TaskCategory> taskcategories = new Set();
     Task(this.summary, [this.scheduled=null]) {
       this.timestamp = new DateTime.now().millisecondsSinceEpoch;
     }
  
positive.code: library task;
  
  import 'dart:convert';
  
  class TaskNote {
    String notebody;
  
negative.code:     tasknotes.add(note);
    }
    
    void addCategory(TaskCategory cat ) {
      taskcategories.add(cat);
    }
    void removeCategory(TaskCategory cat) {
      taskcategories.remove(cat);
    }
  }
  