flutter のエラーに立ち向かう

$ flutter run

...
/usr/local/Caskroom/flutter/1.22.5/flutter/.pub-cache/hosted/pub.dartlang.org/intl-0.17.0-nullsafety.2/lib/src/intl/number_parser.dart:183:44: Error: This requires the null safety language feature, which is experimental.
You can enable the experiment using the '--enable-experiment=non-nullable' command line option.
        _normalized.write(replacements[key]!());                        
                                           ^                            
/usr/local/Caskroom/flutter/1.22.5/flutter/.pub-cache/hosted/pub.dartlang.org/intl-0.17.0-nullsafety.2/lib/src/intl/number_parser.dart:237:8: Error: This requires the null safety language feature, which is experimental.
You can enable the experiment using the '--enable-experiment=non-nullable' command line option.
    num? parsed = int.tryParse(normalizedText);                         
       ^                                                                
                                                                        
                                                                        
FAILURE: Build failed with an exception.                                
                                                                        
* Where:                                                                
Script '/usr/local/Caskroom/flutter/1.22.5/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 904
                                                                        
* What went wrong:                                                      
Execution failed for task ':app:compileFlutterBuildDebug'.              
> Process 'command '/usr/local/Caskroom/flutter/1.22.5/flutter/bin/flutter'' finished with non-zero exit value 1
                                                                        
* Try:                                                                  
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
                                                                        
* Get more help at https://help.gradle.org                              
                                                                        
BUILD FAILED in 22s                                                     
Running Gradle task 'assembleDebug'...                                  
Running Gradle task 'assembleDebug'... Done                        24.0s
Exception: Gradle task assembleDebug failed with exit code 1

> flutter clear
> flutter pub get
> flutter run