[ERROR] Queries returning single elements might return null.

This is on and off bug I noticed, something it works something it does, I removed the build, pubspec.lock, flutter clean, flutter doctor, flutter pub get, still not working, any way to fix it?, thank you.

even better if any way that I can debug it myself? thank you

dependencies
    sqflite: any

dev_dependencies:
  flutter_test:
    sdk: flutter
  floor_generator: ^1.4.0
  build_runner: ^2.1.2

Here is my @dao code

@Query("select  * from Staffs  where id = :id;")
  Future<Staff?>findStaffById(int id);

  @Query("select * from Staffs where email = :email;")
  Future<Staff?>findStaffByEmail(String email);

Here is console error log

Queries returning single elements might return null. Make the method return a Future of a nullable type e.g. Future<Person?>.
package:i_can_fly/dao/staff-dao.dart:11:17
   ╷
11 │   Future<Staff?>findStaffById(int id);
   │                 ^^^^^^^^^^^^^
   ╵
package:floor_generator/processor/query_method_processor.dart 140:9  QueryMethodProcessor._assertReturnsNullableSingle
package:floor_generator/processor/query_method_processor.dart 53:5   QueryMethodProcessor.process
package:floor_generator/processor/dao_processor.dart 91:15           DaoProcessor._getQueryMethods.<fn>
dart:core                                                            Iterable.toList
package:floor_generator/processor/dao_processor.dart 92:10           DaoProcessor._getQueryMethods
package:floor_generator/processor/dao_processor.dart 55:26           DaoProcessor.process
package:floor_generator/processor/database_processor.dart 89:9       DatabaseProcessor._getDaoGetters.<fn>
dart:core                                                            Iterable.toList
package:floor_generator/processor/database_processor.dart 92:8       DatabaseProcessor._getDaoGetters
package:floor_generator/processor/database_processor.dart 36:24      DatabaseProcessor.process
package:floor_generator/generator.dart 72:39                         FloorGenerator._getDatabase
package:floor_generator/generator.dart 26:22                         FloorGenerator.generateForAnnotatedElement
package:source_gen/src/generator_for_annotation.dart 61:30           GeneratorForAnnotation.generate
package:source_gen/src/builder.dart 342:33                           _generate
dart:async                                                           Stream.toList.<fn>
package:source_gen/src/builder.dart 107:9                            _Builder._generateForLibrary
package:source_gen/src/builder.dart 99:5                             _Builder.build

pinchbv / floor

[ERROR] Queries returning single elements might return null. #837