CancellableHandler constructor Null safety

1. nevis_mobile_authentication_sdk
2. nevis_mobile_authentication_sdk
3. CancellableHandler
4. CancellableHandler constructor

CancellableHandler class

1. Constructors
2. CancellableHandler
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. cancel
8. noSuchMethod
9. toString
10. Operators
11. operator ==