Kotlin DatabaseManager_Impl 不是抽象的，不会覆盖 RoomDatabase 中的抽象方法 clearAllTables()

当我构建这段代码时，它显示了构建错误:

DatabaseManager_Impl is not abstract and does not override abstract method clearAllTables() in RoomDatabase.

build.gradle:

implementation 'android.arch.persistence.room:runtime:1.0.0'
kapt 'android.arch.persistence.room:compiler:1.0.0'
implementation 'android.arch.persistence.room:rxjava2:1.0.0'
implementation 'android.arch.persistence.room:guava:1.1.0-beta3'

按照房间指南实施数据库:

@Database(entities = {Task.class}, version = 1)
public abstract class DatabaseManager extends RoomDatabase {
    private static final String DATABASE =
                         Iterables.getLast(Splitter.on(".").trimResults().split(BuildConfig.APPLICATION_ID)).concat("-db");
    private static volatile DatabaseManager instance;

    public abstract TaskDao taskDao();

    synchronized public static DatabaseManager onInstance(Context context)     {
        if (instance == null) {
            instance = newInstance(context, false);
        }
        return instance;
    }

    public static DatabaseManager newInstance(Context context, boolean memoryOnly) {
        RoomDatabase.Builder<DatabaseManager> builder;

        if (memoryOnly) {
            builder = Room.inMemoryDatabaseBuilder(context.getApplicationContext(), DatabaseManager.class);
        } else {
            builder = Room.databaseBuilder(context.getApplicationContext(), DatabaseManager.class, DATABASE);
        }

        return builder.fallbackToDestructiveMigration().build();
    }

}