factory property Null safety

1. jrpn
2. jrpn16.main
3. ButtonLayout16
4. factory property

ButtonLayout16 class

1. Constructors
2. ButtonLayout16
3. Properties
4. a
5. b
6. bin
7. bsp
8. c
9. chs
10. d
11. dec
12. div
13. dot
14. e
15. enter
16. f
17. factory
18. fShift
19. gsb
20. gShift
21. gto
22. hashCode
23. hex
24. landscapeLayout
25. minus
26. mult
27. n0
28. n1
29. n2
30. n3
31. n4
32. n5
33. n6
34. n7
35. n8
36. n9
37. oct
38. onOff
39. plus
40. portraitLayout
41. rcl
42. rdown
43. rs
44. runtimeType
45. sst
46. sto
47. xy
48. Methods
49. noSuchMethod
50. toString
51. Operators
52. operator ==