Null Safety

[arvind-iyer-2001]

Most of the Code here is based on Flutter 1 Version and Flutter 2 Version has Sound Null Safety
The Code needs to be updates to meet the requirements of the most recent Flutter Version.

[FilledStacks]

@arvind-iyer-2001 You can go through and update all the tutorials to null safe and make a PR and I'll review and merge it in.