AverageList<T extends num> constructor Null safety

1. smooth_app
2. collections_helper
3. AverageList<T extends num>
4. AverageList constructor

AverageList class

1. Constructors
2. AverageList
3. Properties
4. first
5. hashCode
6. isEmpty
7. isNotEmpty
8. iterator
9. last
10. length
11. reversed
12. runtimeType
13. single
14. Methods
15. add
16. addAll
17. any
18. asMap
19. average
20. cast
21. clear
22. contains
23. elementAt
24. every
25. expand
26. fillRange
27. firstWhere
28. fold
29. followedBy
30. forEach
31. getRange
32. indexOf
33. indexWhere
34. insert
35. insertAll
36. join
37. lastIndexOf
38. lastIndexWhere
39. lastWhere
40. map
41. noSuchMethod
42. reduce
43. remove
44. removeAt
45. removeLast
46. removeRange
47. removeWhere
48. replaceRange
49. retainWhere
50. setAll
51. setRange
52. shuffle
53. singleWhere
54. skip
55. skipWhile
56. sort
57. sublist
58. take
59. takeWhile
60. toList
61. toSet
62. toString
63. where
64. whereType
65. Operators
66. operator +
67. operator ==
68. operator []
69. operator []=