EventSinkBase<T> constructor Null safety

1. Flutter
2. async
3. EventSinkBase<T>
4. EventSinkBase constructor

EventSinkBase class

1. Constructors
2. EventSinkBase
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. add
8. addError
9. close
10. noSuchMethod
11. onAdd
12. onClose
13. onError
14. toString
15. Operators
16. operator ==