preferred_size_widget library Null safety

1. flutter_json_widgets
2. preferred_size_widget library

flutter_json_widgets package

1. Libraries
2. alignment
3. border_radius
4. border_side
5. box_constraints
6. callback
7. color
8. color_filter
9. color_scheme
10. colors
11. curves
12. data_cell
13. data_column
14. data_row
15. decoration
16. decoration_image
17. dropdown_menu_item
18. edge_insets
19. enums
20. floating_action_button_location
21. floating_label_alignment
22. flutter
23. flutter_json_widgets
24. flutter_widget
25. font_feature
26. font_variation
27. font_weight
28. form_data
29. gradient
30. gradient_transform
31. icon_data
32. icon_theme_data
33. icons
34. image_provider
35. inline_span
36. input_decoration
37. key
38. locale
39. material_banner
40. material_state_property
41. matrix_4
42. mouse_cursor
43. navigation_rail_destination
44. network_request
45. offset
46. paint
47. popup_menu_entry
48. preferred_size_widget
49. radius
50. rect
51. scroll_physics
52. shadow
53. shape_border
54. size
55. sliver
56. sliver_child_delegate
57. sliver_grid_delegate
58. snack_bar
59. snack_bar_action
60. strut_style
61. table_border
62. table_column_width
63. table_row
64. text_align_vertical
65. text_decoration
66. text_height_behavior
67. text_input_formatter
68. text_input_type
69. text_style
70. text_theme
71. theme_data
72. visual_density
73. widget