Not able to update localizations

[MatsAndT]

Hi, I am trying to run dart update_localizations.dart, but I keep getting this error you see below.

update_localizations.dart: Warning: Interpreting this as package URI, 'package:rotary_game_app/helpers/update_localizations.dart'.
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:35:52: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
Future<Response> head(Uri url, {Map<String, String>? headers}) =>
                                                   ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:45:51: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
Future<Response> get(Uri url, {Map<String, String>? headers}) =>
                                                  ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:67:29: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                            ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:67:46: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                                             ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:67:62: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                                                             ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:90:29: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                            ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:90:46: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                                             ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:90:62: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                                                             ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:114:29: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>
                            ^
../../../../../../development/flutter/.pub-cache/hosted/pub.dartlang.org/http-0.13.3/lib/http.dart:114:46: Error: This requires the 'non-nullable' experiment to be enabled.
Try enabling this experiment by adding it to the command line when compiling and running.
        {Map<String, String>? headers, Object? body, Encoding? encoding}) =>

Any idea on why? The lib version is the same as the default. dart --version : Dart VM version: 2.7.0 (Fri Dec 6 16:26:51 2019 +0100) on "macos_x64"

PS: Thank you for the repo!

[delay]

Are you using a version of dart that supports null safety. This is the error, maybe try searching for that. ‘This requires the 'non-nullable' experiment to be enabled. Try enabling this experiment by adding it to the command line when compiling and running.’