Fatal error when encoding a Model with an non-initialised OptionalParent relation

[tarag]

If a Model contains an OptionalParent relation that is not initialised to nil in the constructor, it will crash with a fatal error when encoding the model after creation of a new instance.

Fatal error: Cannot access field before it is initialized or fetched: todo_id: file .../fluent-kit/Sources/FluentKit/Properties/Field.swift, line 21

Example based on Vapor 4 template:

Model

final class TodoGroup: Model, Content {
    static let schema = "todo_groups"

    @ID(key: .id)
    var id: UUID?

    @Field(key: "title")
    var title: String

    init() { }
    
    @OptionalParent(key: "todo_id")
    public var todo: Todo?
}

Controller method that crashes upon encoding the response:

    func create(req: Request) throws -> EventLoopFuture<TodoGroup> {
        let group = TodoGroup()
        group.title = "My New Todo Group"
        return group.save(on: req.db).map { group }
    }

Of course the workaround to initialise all relations in the constructor is simple but the consequence if it is forgotten seems severe.

vapor: 4.0.0-rc.3.12
fluent-kit: 1.0.0-rc.1.13

[tanner0101]

This has been fixed in #270. @OptionalParent will now return nil when it is uninitialized.