item property Null safety

1. jrpn
2. view.back_panel
3. BPCell
4. item property

BPCell class

1. Constructors
2. BPCell
3. Properties
4. eraseBottom
5. hashCode
6. item
7. runtimeType
8. width
9. Methods
10. noSuchMethod
11. paint
12. toString
13. Operators
14. operator ==