struct Beacon: Hashable, Codable, Identifiable {
    var id: Int
    ...
    var beaconadv: BeaconAdv
    ...
}

struct BeaconAdv: Hashable, Codable {
    ...
    var booltest: Bool?
    ...
}

final class UserData: BindableObject {

    let willChange = PassthroughSubject<UserData, Never>()

    var showFavoritesOnly = false {
        willSet {
            willChange.send(self)
        }
    }

    var showOtherBeacons = true {
        didSet {
            willChange.send(self)
        }
    }

    var updateBeaconDetails = true {
        didSet {
            willChange.send(self)
        }
    }

    var beacons = beaconData {
        didSet {
            willChange.send(self)
        }
    }
}

let beaconData: [Beacon] = load("beaconDataTest.json")

private var centralManager : CBCentralManager!
private var locationManager : LocationManager!
var userData: UserData!

public func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {

struct BeaconDetail: View {
    @EnvironmentObject var userData: UserData
    ...
    var body: some View {
        VStack {
            List {

                Section() {
                    if self.userData.beacons[self.beaconIndex].beaconadv.booltest != nil {
                        if self.userData.beacons[self.beaconIndex].beaconadv.booltest! {
                            Text("booltest = true")
                        } else {
                            Text("booltest = false")
                        }
                    } else {
                        Text("booltest = nil")
                    }
                }
                ...
        }
     ...       .navigationBarTitle(Text(self.userData.beacons[self.beaconIndex].name), displayMode: .inline)
            .background(Color.white)
            .listStyle(.grouped)
    }
}

Thread 1: EXC_BREAKPOINT (code=1, subcode=0x1d3b0b690)

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.

        return true
    }