Error al usar flutter_launcher_icons

Al ejecutar flutter

flutter pub run flutter_launcher_icons:main

aparece este error

  ════════════════════════════════════════════
     FLUTTER LAUNCHER ICONS (v0.9.1)                               
  ════════════════════════════════════════════
  

✓ Successfully generated launcher icons
Unhandled exception:
FormatException: Invalid number (at character 1)

^

#0      int._handleFormatError (dart:core-patch/integers_patch.dart:129:7)
#1      int.parse (dart:core-patch/integers_patch.dart:55:14)
#2      minSdk (package:flutter_launcher_icons/android.dart:309:18)
#3      createIconsFromConfig (package:flutter_launcher_icons/main.dart:94:47)
#4      createIconsFromArguments (package:flutter_launcher_icons/main.dart:60:7)
#5      main (file:///home/lmayta/snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_launcher_icons-0.9.2/bin/main.dart:6:26)
#6      _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:295:32)
#7      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:192:12)

Se soluciono modificando este archivo

vim snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_launcher_icons-0.9.2/lib/android.dart

// final String minSdk = line.replaceAll(RegExp(r'[^\d]'), '');
// To this:
final String minSdk = "21"; // line.replaceAll(RegExp(r'[^\d]'), '');

y en android/app/build.gradle

    defaultConfig {
        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
        applicationId "com.example.flutter_familia"
        minSdkVersion 21
        targetSdkVersion flutter.targetSdkVersion
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
    }