BoxParentData constructor Null safety

1. Flutter
2. rendering
3. BoxParentData
4. BoxParentData constructor

BoxParentData class

1. Constructors
2. BoxParentData
3. Properties
4. hashCode
5. offset
6. runtimeType
7. Methods
8. detach
9. noSuchMethod
10. toString
11. Operators
12. operator ==