onStart method Null safety

1. baguette
2. Screen
3. Screen<T extends ScreenWidget>
4. onStart method

Screen class

1. Constructors
2. Screen
3. Properties
4. context
5. hashCode
6. mounted
7. runtimeType
8. widget
9. Methods
10. activate
11. build
12. buildContent
13. buildDrawer
14. buildNavigationBar
15. buildToolBar
16. createTicker
17. deactivate
18. debugFillProperties
19. didChangeAccessibilityFeatures
20. didChangeAppLifecycleState
21. didChangeDependencies
22. didChangeLocales
23. didChangeMetrics
24. didChangePlatformBrightness
25. didChangeTextScaleFactor
26. didHaveMemoryPressure
27. didPopRoute
28. didPushRoute
29. didPushRouteInformation
30. didUpdateWidget
31. dispose
32. getViewModel
33. initState
34. isShowActivity
35. noSuchMethod
36. notifyChanges
37. onCreate
38. onDispose
39. onPause
40. onResume
41. onStart
42. onStop
43. reassemble
44. setState
45. setViewModel
46. showActivity
47. toDiagnosticsNode
48. toString
49. toStringShort
50. Operators
51. operator ==