MessengerKey constructor Null safety

1. baguette
2. MessengerKey
3. MessengerKey
4. MessengerKey constructor

MessengerKey class

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