ICommandGroup constructor Null safety

1. nyxx_commander
2. nyxx_commander
3. ICommandGroup
4. ICommandGroup constructor

ICommandGroup class

1. Constructors
2. ICommandGroup
3. Properties
4. afterHandler
5. aliases
6. beforeHandler
7. commandEntities
8. commandNames
9. defaultHandler
10. hashCode
11. name
12. parent
13. runtimeType
14. Methods
15. getFullCommandMatch
16. isEntityName
17. noSuchMethod
18. registerCommandEntity
19. registerCommandGroup
20. registerDefaultCommand
21. registerSubCommand
22. toString
23. Operators
24. operator ==