我已经添加// @dart=2.9到我的所有文件中，但build_runner不会在不抛出此错误的情况下做它的事情：
Warning: Operand of null-aware operation '?.' has type 'SendPort' which excludes null. - 'SendPort' is from 'dart:isolate'. sendPort?.send(result); ^Error: Cannot run with sound null safety, because the following dependencies don't support null safety:
- package:build_runner_core
- package:json_serializable
- package:moor_generator
- package:objectbox_generator
- package:retrofit_generator
- package:source_gen
- package:build_config
- package:build_runner
- package:build
- package:json_annotation
- package:glob
- package:pool
- package:crypto
- package:logging
- package:watcher
- package:build_resolvers
- package:timing
- package:graphs
- package:package_config
- package:yaml
- …