BPItem constructor Null safety

1. jrpn
2. view.back_panel
3. BPItem
4. BPItem constructor

BPItem class

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