messageID property Null safety

1. baguette
2. Message
3. Message
4. messageID property

Message class

1. Constructors
2. Message
3. Properties
4. conversationID
5. date
6. hashCode
7. memberID
8. message
9. messageID
10. runtimeType
11. Methods
12. noSuchMethod
13. toString
14. Operators
15. operator ==