ICommandGroup<T extends IContext> constructor Null safety

1. nyxx_commands
2. nyxx_commands
3. ICommandGroup<T extends IContext>
4. ICommandGroup constructor

ICommandGroup class

1. Constructors
2. ICommandGroup
3. Properties
4. checks
5. children
6. hashCode
7. onPostCall
8. onPreCall
9. options
10. runtimeType
11. Methods
12. addCommand
13. check
14. getCommand
15. noSuchMethod
16. toString
17. walkCommands
18. Operators
19. operator ==