AuthenticateEventHandler constructor Null safety

1. sendbird_sdk
2. authenticate_event_handler
3. AuthenticateEventHandler
4. AuthenticateEventHandler constructor

AuthenticateEventHandler class

1. Constructors
2. AuthenticateEventHandler
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. handleWithAuthInfo
8. noSuchMethod
9. onFinishAuthentication
10. toString
11. Operators
12. operator ==