guard let mainUrl = Bundle.main.url(forResource: "Athletes", withExtension: "json") else { return }

do {
    let documentDirectory = try fm.url(for: .documentDirectory, in: .userDomainMask, appropriateFor:nil, create:false)
    let subUrl = documentDirectory.appendingPathComponent("Athletes.json")
    loadFile(mainPath: mainUrl, subPath: subUrl)
} catch {
    print(error)
}