RECEIVE_MESSAGE constant Null safety

1. baguette
2. NotificationsKey
3. NotificationsKey
4. RECEIVE_MESSAGE 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