我得到了这个错误时，试图安装geoflutterfire的终端。但我的SDK比2.12.0高。

ben@MacBook projectva % flutter pub add geoflutterfire
The current Dart SDK version is 3.0.3.

Because geoflutterfire >=3.0.0-nullsafety.1 <3.0.0-nullsafety.3 depends on rxdart ^0.26.0 and geoflutterfire >=3.0.0-nullsafety.3 <3.0.1 depends on cloud_firestore ^2.0.0, geoflutterfire
  >=3.0.0-nullsafety.1 <3.0.1 requires rxdart ^0.26.0 or cloud_firestore ^2.0.0.
And because geoflutterfire <2.2.3 doesn't support null safety, geoflutterfire <2.2.3-∞ or >=3.0.0-nullsafety.1 <3.0.1-∞ requires rxdart ^0.26.0 or cloud_firestore ^2.0.0.
And because geoflutterfire >=2.2.3 <3.0.0-nullsafety.1 depends on cloud_firestore ^3.1.6 and geoflutterfire >=3.0.1 <3.0.2 depends on cloud_firestore ^2.3.0, geoflutterfire <3.0.2 requires
  rxdart ^0.26.0 or cloud_firestore >=2.0.0 <3.0.0 or ^3.1.6.
And because geoflutterfire >=3.0.2 depends on cloud_firestore ^3.1.6 and okleva depends on cloud_firestore ^4.7.0, every version of geoflutterfire requires rxdart ^0.26.0.
So, because okleva depends on both rxdart ^0.27.7 and geoflutterfire any, version solving failed.

The lower bound of "sdk: '>=2.0.0-dev.28.0 <3.0.0'" must be 2.12.0 or higher to enable null safety.
For details, see https://dart.dev/null-safety

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我在pubspec.yaml cloud_firestore上的版本：^4.7.0 rxdart：0.27.7
我试图寻找一个解决方案来改变Dart SDK，但我发现在Dart 3中，空安全是内置的;你不能关掉它。(https://dart-ko.dev/resources/dart-3-migration)
有人能帮忙解决这个问题吗。然后安装geoflutterfire？先谢谢你。