         error: NSError?
         ) {
             if let error = error {
-                errorCompletion?(error)
+                _error?(error)
                 finishWithError(error)
                 
                 return

                let json = try NSJSONSerialization.JSONObjectWithData(data,
                    options: .MutableContainers
                    ) as? [String:AnyObject]
                completion?(json)
            } catch let error as NSError {
                errorCompletion?(error)
                finishWithError(error)
                
                return

}

public class DownloadJSONOperation: GroupOperation {
    // MARK: - Private Properties
    private let _error: (NSError -> Void)?
    private let _completion: ([String:AnyObject]? -> Void)?
    
    private var composedEndpointURL: NSURL {
        let (endpoint, params) = self.composedEndpoint
