NotFoundError constructor Null safety

1. sendbird_sdk
2. error
3. NotFoundError
4. NotFoundError constructor

NotFoundError class

1. Constructors
2. NotFoundError
3. Properties
4. code
5. hashCode
6. message
7. runtimeType
8. stackTrace
9. Methods
10. byaction
11. noSuchMethod
12. toJson
13. toString
14. Operators
15. operator ==