Swift5-FlattenNestedOptionalResultingFromTry.swift

struct Car {
    var id: Int
    init?(id: Int) {
        guard id > 0 else {
             return nil
             }
        self.id = id
    }
    
    func checkSystemWhenStart() throws -> String {
        // If have error then return error message
        // Else return empty string
        // Case can't check system health, throws
        return ""
    }
}
let car = Car(id: 1)
let errorMessage = try? car?.checkSystemWhenStart()
print(type(of:errorMessage))