I am having problem loading swiftData model items in List

here is my 2 model

@Model
final class Category: Identifiable,Hashable {
    @Attribute(.unique) var uniqueID: String
    var name: String
    var iconName: String

    var subCategories : [Subcategory]? = []

    init(name: String, iconName: String) {
        self.uniqueID = UUID().uuidString
        self.name = name
        self.iconName = iconName
    }

    func hash(into hasher: inout Hasher) {
        hasher.combine(uniqueID)
    }
}

@Model
final class Subcategory: Identifiable,Hashable {
    @Attribute(.unique) var uniqueID: String
    @Relationship(inverse: \Category.subCategories) var category: Category
    var name: String
    var iconName: String

    init(category: Category, name: String, iconName: String) {
        self.category = category
        self.uniqueID = UUID().uuidString
        self.name = name
        self.iconName = iconName
    }

    func hash(into hasher: inout Hasher) {
        hasher.combine(uniqueID)
    }

}

This is how i am creating my List

  List {
      OutlineGroup(viewModel.categories, children: \.subCategories) { category in
          CategoryCell(category: category)
      }
  }

I have double checked the sub categories are coming with the FetchRequest but give me Failed to produce diagnostic for expression; please submit a bug report error when I try to create list