how decompress File by calling compression file using HUFFMAN

Question

I want to build a file compression using Huffman. When I run the program compress and decompress the file it's OK. I close the program. After closing the program I open the program again. Then I only call the compression file which stores the bit sequence to decompress. But then it shows the null pointer exception. How can I solve it?? Below This are the compression and decompression code. I save the compression bit into a byte array. This works fine. but the problem arises when I only compress the file and close the program. Then if I want to decompress the file by calling the compression file by running the program again it shows me the null pointer exception. the exception is:

Exception in thread "main" java.lang.NullPointerException
at compress.Decode.decode(Decode.java:25)
at compress.MainClasss.main(MainClasss.java:133)

C:\Users\Tech Land\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1

public class MainClasss {

public static void main(String[] args) throws IOException {
    String s = "";
    String test = "";
    String decodee = "";
       Scanner scan = new Scanner(System.in);
       while(true){
         System.out.println("pls write the file name");
    //   String binaryString ="";
      String name = scan.next();
  
   
    try {

        test = new String(Files.readAllBytes(Paths.get("C://Users//Tech Land//Desktop//" + name))); //first read the java file as a string
    } //first read the java file as a string
    catch (IOException e) {

        e.printStackTrace();
    }
      
  
    String de = scan.next();
    if (de.equals("com")) {
        Encode ob = new Encode();
        s = ob.encode(test);
        BitSet bitset = new BitSet(s.length());

        int bitcounter = 0;
        for (Character c : s.toCharArray()) {
            if (c.equals('1')) {
                bitset.set(bitcounter);
            }
            bitcounter++;
        }

        FileOutputStream t = new FileOutputStream("C://Users//Tech Land//Desktop//" + name, false);
        t.write(bitset.toByteArray());
        System.out.println("file successfully compressed");

        }
     
    } else if (de.equals("dcom")) {
        try {

            decodee = new String(Files.readAllBytes(Paths.get("C://Users//Tech Land//Desktop//" + name))); //first read the java file as a string
        } //first read the java file as a string
        catch (IOException e) {

            e.printStackTrace();
        }

        String binaryString = "";
        File file = new File("C://Users//Tech Land//Desktop//" + name);
        FileInputStream fin = null;
        try {
            // create FileInputStream object
            fin = new FileInputStream(file);

            byte fileContent[] = new byte[(int) file.length()];

            fin.read(fileContent);
          
            for (int i = 0; i <= BitSet.valueOf(fileContent).length(); i++) {
                if (BitSet.valueOf(fileContent).get(i)) {
                    binaryString += "1";
                } else {
                    binaryString += "0";
                }
            }
            //System.out.println("");
            // System.out.println(""+fileContent.length);

            System.out.println("" + binaryString);
        } catch (Exception e) {
            e.printStackTrace();
        }

        Decode ddecode=new Decode();
        String k=ddecode.decode(binaryString);
          FileWriter fw = new FileWriter("C://Users//Tech Land//Desktop//" + name, false);
             System.out.println("");
          for (int j = 0; j < k.length(); j++) {
              fw.write(k.charAt(j));
         }
          System.out.println("successful");
          fw.close();
           }
         
    }

}