ScreenManager constructor Null safety

1. baguette
2. ScreenManager
3. ScreenManager
4. ScreenManager constructor

ScreenManager class

1. Constructors
2. ScreenManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. addPlugin
8. cleanPlugins
9. getPlugin
10. load
11. noSuchMethod
12. open
13. removePlugin
14. setRouter
15. toString
16. Operators
17. operator ==