TAG constant Null safety

1. baguette
2. NotificationsKey
3. NotificationsKey
4. TAG constant

NotificationsKey class

1. Constructors
2. NotificationsKey
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Constants
12. RECEIVE_MESSAGE
13. TAG