Why use completionHandlerForConvertData closure in the convertDataWithCompletionHandler function？ - ios

Question

Below is code making a request,the completionHandlerForGET was passed to completionHandlerForConvertData handler of function convertDataWithCompletionHandler.But the completionHandlerForConvertData seems doing nothing.Why use it?
func taskForGETMethod(_ method: String, parameters: [String:AnyObject], completionHandlerForGET: #escaping (_ result: AnyObject?, _ error: NSError?) -> Void) -> URLSessionDataTask {
/* 1. Set the parameters */
var parametersWithApiKey = parameters
parametersWithApiKey[ParameterKeys.ApiKey] = Constants.ApiKey as AnyObject?
/* 2/3. Build the URL, Configure the request */
let request = NSMutableURLRequest(url: tmdbURLFromParameters(parametersWithApiKey, withPathExtension: method))
/* 4. Make the request */
let task = session.dataTask(with: request as URLRequest) { (data, response, error) in
func sendError(_ error: String) {
print(error)
let userInfo = [NSLocalizedDescriptionKey : error]
completionHandlerForGET(nil, NSError(domain: "taskForGETMethod", code: 1, userInfo: userInfo))
}
/* GUARD: Was there an error? */
guard (error == nil) else {
sendError("There was an error with your request: \(error!)")
return
}
/* GUARD: Did we get a successful 2XX response? */
guard let statusCode = (response as? HTTPURLResponse)?.statusCode, statusCode >= 200 && statusCode <= 299 else {
sendError("Your request returned a status code other than 2xx!")
return
}
/* GUARD: Was there any data returned? */
guard let data = data else {
sendError("No data was returned by the request!")
return
}
/* 5/6. Parse the data and use the data (happens in completion handler) */
self.convertDataWithCompletionHandler(data, completionHandlerForConvertData: completionHandlerForGET)
}
/* 7. Start the request */
task.resume()
return task
}
The completionHandlerForConvertData isn't doing anything such as printing an error.
private func convertDataWithCompletionHandler(_ data: Data, completionHandlerForConvertData: (_ result: AnyObject?, _ error: NSError?) -> Void) {
var parsedResult: AnyObject! = nil
do {
//class func jsonObject(with data: Data, options opt: JSONSerialization.ReadingOptions = []) throws -> Any
//Returns a Foundation object from given JSON data.
parsedResult = try JSONSerialization.jsonObject(with: data, options: .allowFragments) as AnyObject
} catch {
let userInfo = [NSLocalizedDescriptionKey : "Could not parse the data as JSON: '\(data)'"]
completionHandlerForConvertData(nil, NSError(domain: "convertDataWithCompletionHandler", code: 1, userInfo: userInfo))
}
completionHandlerForConvertData(parsedResult, nil)
}