onTertiary property Null safety

1. flutter_json_widgets
2. color_scheme
3. ColorSchemeFromSeed
4. onTertiary property

ColorSchemeFromSeed class

1. Constructors
2. ColorSchemeFromSeed
3. fromJson
4. Properties
5. background
6. brightness
7. copyWith
8. error
9. errorContainer
10. hashCode
11. inversePrimary
12. inverseSurface
13. onBackground
14. onError
15. onErrorContainer
16. onInverseSurface
17. onPrimary
18. onPrimaryContainer
19. onSecondary
20. onSecondaryContainer
21. onSurface
22. onSurfaceVariant
23. onTertiary
24. onTertiaryContainer
25. outline
26. outlineVariant
27. primary
28. primaryContainer
29. runtimeType
30. scrim
31. secondary
32. secondaryContainer
33. seedColor
34. shadow
35. surface
36. surfaceTint
37. surfaceVariant
38. tertiary
39. tertiaryContainer
40. Methods
41. map
42. mapOrNull
43. maybeMap
44. maybeWhen
45. noSuchMethod
46. toJson
47. toString
48. when
49. whenOrNull
50. Operators
51. operator ==