How to update field from required to optional using vapor (fluent migration)?

I'm use vapor 4

struct MakeRegionOptional: AsyncMigration {
    
    func prepare(on database: Database) async throws {
        try await database.schema("Attraction")
            .updateField("region", .string)
            .update()
    }
    
    func revert(on database: Database) async throws {
        try await database.schema("Attraction")
            .field("region", .sql(.default("")))
            .update()
    }
    
}

also adding migrations in the configuration file update table model.

app.migrations.add(MakeRegionOptional())

// Attraction model for table

final class Attraction: Model, Content {
    static let schema = "Attraction"
    
    @ID(key: .id)
    var id: UUID?
    
    
    //Before
    //@Field(key: "region")
    //var region: String
    
    // after make optional
    @OptionalField(key: "region")
    var region: String?
    
    init() { }
    
    init(id: UUID? = nil, region: String?) {
        self.id = id
        self.region = region
    }
     }

I'm trying to make optional region field using migration. But my code is not working maybe my migration is wrong. Anyone knows how to make working on this migration?

update() enables you to change a column from optional, to .required but not the other way. Something like .notRequired would be useful here, but it doesn't exist!

The easiest way is to use a raw sql query to alter the column.