getRootContext method Null safety

1. baguette
2. ContextManager
3. ContextManager
4. getRootContext method

ContextManager class

1. Constructors
2. ContextManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. addPlugin
8. cleanPlugins
9. getPlugin
10. getRootContext
11. getRootKey
12. noSuchMethod
13. removePlugin
14. toString
15. Operators
16. operator ==