listItemStyle property Null safety

1. animated_custom_dropdown
2. animated_custom_dropdown
3. CustomDropdown
4. listItemStyle property

CustomDropdown class

1. Constructors
2. CustomDropdown
3. search
4. Properties
5. borderRadius
6. borderSide
7. canCloseOutsideBounds
8. controller
9. errorBorderSide
10. errorStyle
11. errorText
12. excludeSelected
13. fieldSuffixIcon
14. fillColor
15. hashCode
16. hintStyle
17. hintText
18. items
19. key
20. listItemBuilder
21. listItemStyle
22. onChanged
23. runtimeType
24. searchType
25. selectedStyle
26. Methods
27. createElement
28. createState
29. debugDescribeChildren
30. debugFillProperties
31. noSuchMethod
32. toDiagnosticsNode
33. toString
34. toStringDeep
35. toStringShallow
36. toStringShort
37. Operators
38. operator ==