Error in SwiftData migrationPlan execution

I'm testing the new SwiftData to see if I can use it on one of my apps. Specifically I'm trying to learn how to use the schema migrations.

I made a new project using Xcode 15 beta 4. I selected to use SwiftData and iCloud.

I ran the generated project and I added a couple of items to the screen.

Then, I wanted to make a schema migration, so I changed the Item model from:

@Model
final class Item {
    var timestamp: Date
    
    init(timestamp: Date) {
        self.timestamp = timestamp
    }
}

to also include a string title:

@Model
final class Item {
    var timestamp: Date
    var title: String
    
    init(timestamp: Date, title: String) {
        self.timestamp = timestamp
        self.title = title
    }
}

I also made some changes to the SwiftUI code to include an empty string when adding a new item, so it could compile:

let newItem = Item(timestamp: Date(), title: "")

And then I added a new file containing the migration, according to what I saw on the video sessions:

//
//  SwiftDataMigrations.swift
//  Test 1
//
//  Created by Diego on 12/07/23.
//

import Foundation
import SwiftData

enum ItemSchemaV1: VersionedSchema {
    static var versionIdentifier: String?
    
    static var models: [any PersistentModel.Type] {
        [Item.self]
    }

    @Model
    final class Item {
        var timestamp: Date
        
        init(timestamp: Date) {
            self.timestamp = timestamp
        }
    }
}

enum ItemSchemaV2: VersionedSchema {
    static var versionIdentifier: String?
    
    static var models: [any PersistentModel.Type] {
        [Item.self]
    }

    @Model
    final class Item {
        var timestamp: Date
        var title: String
        
        init(timestamp: Date, title: String) {
            self.timestamp = timestamp
            self.title = title
        }
    }
}

enum ItemsMigrationPlan: SchemaMigrationPlan {
    static var schemas: [any VersionedSchema.Type] {
        [ItemSchemaV1.self, ItemSchemaV2.self]
    }
    
    static var stages: [MigrationStage] {
        [migrateV1toV2]
    }
    
    static let migrateV1toV2 = MigrationStage.lightweight(fromVersion: ItemSchemaV1.self, toVersion: ItemSchemaV2.self)
}

After that, I specified the migrationPlan in the app:

//
//  Test_1App.swift
//  Test 1
//
//  Created by Diego on 12/07/23.
//

import SwiftUI
import SwiftData

@main
struct Test_1App: App {
    var container = try! ModelContainer(
        for: Item.self,
        migrationPlan: ItemsMigrationPlan.self
    )

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .modelContainer(container)
    }
}

And then I tried to run the app but it crashed on launch with this error:

SwiftData/ModelContext.swift:179: Fatal error: Container does not have any data stores

Does anyone have any idea about what I might be missing?

The only thing that didn't matched the videos was that when creating a ModelContainer, the code on the video showed var container = ModelContainer... but the compiler showed the error Call can throw, but errors cannot be thrown out of a property initializer, so I added the try!. Also, on the VersionedSchema, I had to add static var versionIdentifier: String?.

Other than that I have no idea.

Thanks in advance.