expiryDate property Null safety

1. baguette
2. TokenUnit
3. TokenUnit
4. expiryDate property

TokenUnit class

1. Constructors
2. TokenUnit
3. fromJson
4. Properties
5. expiryDate
6. hashCode
7. runtimeType
8. token
9. Methods
10. noSuchMethod
11. toJson
12. toString
13. Operators
14. operator ==