4 пункт не проходит, я не знаю что не так и где я ошибся. помогите пожалуйста 
public class Solution {
    public static Map<String, Integer> resultMap = new HashMap<String, Integer>();

    public static void main(String[] args) throws IOException {
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
        String fileName = null;
        while (!"exit".equals((fileName = bufferedReader.readLine()))) {
            new ReadThread(fileName).start();
        }
    }

    public static class ReadThread extends Thread {
        private String fileName;

        public ReadThread(String fileName) {
            this.fileName = fileName;
        }
        @Override
        public void run() {
            try (FileInputStream fileInputStream = new FileInputStream(fileName)) {
                TreeMap<Byte, Integer> map = new TreeMap<Byte, Integer>();

                byte[] bytes = new byte[fileInputStream.available()];
                while(fileInputStream.available() > 0)
                    fileInputStream.read(bytes);

                for (byte curByte : bytes) {
                    if (map.get(curByte) == null) {
                        map.put(curByte, Collections.frequency(Arrays.asList(bytes), curByte));
                    }
                }

                for (Map.Entry<Byte, Integer> entry : map.entrySet()) {
                    if (entry.getValue() == map.get(map.lastKey())) {
                        resultMap.put(fileName, (int)entry.getKey());
                    }
                }
            }
            catch(IOException ioException) {
                System.out.println(ioException.getMessage());
            }
        }
    }
}