entrace property Null safety

1. flutter_baidu_mapapi_search
2. flutter_baidu_mapapi_search
3. BMFWalkingStep
4. entrace property

BMFWalkingStep class

1. Constructors
2. BMFWalkingStep
3. fromMap
4. Properties
5. direction
6. distance
7. duration
8. entrace
9. entraceInstruction
10. exit
11. exitInstruction
12. hashCode
13. instruction
14. name
15. points
16. pointsCount
17. runtimeType
18. Methods
19. fromMap
20. noSuchMethod
21. toMap
22. toString
23. Operators
24. operator ==