getThemeMode abstract method Null safety

1. baguette
2. IEnvironmentManager
3. IEnvironmentManager
4. getThemeMode abstract method

IEnvironmentManager class

1. Constructors
2. IEnvironmentManager
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. addPlugin
8. cleanPlugins
9. getBaseUrl
10. getBuild
11. getCurrency
12. getDeviceID
13. getDeviceModel
14. getEnvironment
15. getGoogleApiKey
16. getLocale
17. getMode
18. getPlatform
19. getPlugin
20. getThemeMode
21. getVersion
22. isDebug
23. noSuchMethod
24. removePlugin
25. restart
26. setCurrency
27. setDebug
28. setLocale
29. setMode
30. setThemeMode
31. toString
32. Operators
33. operator ==