В чем ошибка

package com.javarush.task.task31.task3101;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.*;
import java.nio.file.attribute.BasicFileAttributes;
import java.util.EnumSet;
import java.util.Map;
import java.util.TreeMap;
import java.util.*;

/*
Проход по дереву файлов
*/

public class Solution {
    public static void main(String[] args) {
        String path = args[0];
        String resultFileAbsolutePath = args[1];


        File file = new File(resultFileAbsolutePath);
        File dest = new File(file.getParent() + "/allFilesContent.txt");
        if (FileUtils.isExist(dest)) {
            //File axuet = new File(resultFileAbsolutePath);
            FileUtils.deleteFile(dest);
        }
        FileUtils.renameFile(file, dest);


        Set<String> result = new TreeSet<>();
        Queue<File> fileTree = new LinkedList<>();


        File rootDir = new File(path);
        Collections.addAll(fileTree, rootDir.listFiles());

        while (!fileTree.isEmpty()) {
            File currentFile = fileTree.poll();
            if (currentFile.isDirectory()) {
                Collections.addAll(fileTree, currentFile.listFiles());
            } else if (currentFile.length() < 50) {
                result.add(currentFile.getName());
            }
        }

        try (FileOutputStream fos = new FileOutputStream(dest)) {
            for (String name : result) {
                fos.write(name.getBytes());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }


    }
}

while (!fileTree.isEmpty()) {
    File currentFile = fileTree.poll();
    if (currentFile.isDirectory()) {
        Collections.addAll(fileTree, currentFile.listFiles());
    } else if (currentFile.length() < 50) {
        result.add(currentFile.getName());
    }
}