toJson method Null safety

1. baguette
2. Value
3. Value
4. toJson method

Value class

1. Constructors
2. Value
3. fromJson
4. Properties
5. android
6. development
7. hashCode
8. ios
9. production
10. runtimeType
11. Methods
12. noSuchMethod
13. toJson
14. toString
15. Operators
16. operator ==