fileType property Null safety

1. sendbird_sdk
2. scheduled_file_message_params
3. ScheduledFileMessageParams
4. fileType property

ScheduledFileMessageParams class

1. Constructors
2. withFile
3. withUrl
4. Properties
5. apnsBundleId
6. appleCriticalAlertOptions
7. customType
8. data
9. dedupId
10. fileType
11. hashCode
12. isSilent
13. markAsRead
14. mentionedUserIds
15. mentionType
16. metaArrays
17. name
18. pushOption
19. reqId
20. requiredAuth
21. runtimeType
22. scheduledAt
23. sendPush
24. size
25. thumbnailSizes
26. uploadFile
27. Methods
28. noSuchMethod
29. toJson
30. toString
31. Operators
32. operator ==