Null safety support

[behnamsattar]

Flutter 2.0 is out and there are apps waiting for packages to migrate to a null safe version. Please consider adding this ASAP.

Yes, the lack of null safety makes this package outdated

[Vishal-Isharani]

@DenisBarzanov @behnamsattar @jeanluc243 added support to null safety in this pr #13
@jeanluc243 Thank you for Great work.

[behnamsattar]

@jeanluc243 is this package still maintained?

[jeanluc243]

Null safety support has been added by upgrading Flutter and Dart to their latest versions.
Dart version 3.9.2