List in-place sort and de-duplicate in Java

Given below code and implement your method (my_method) which will remove the duplicates and sort the list.

Given following conditions

Implement my_method which does an in place modification to the list
Remove the duplicate and assign to null/empty

import java.io.*;
import java.util.*;
class Solution {
  public static void main(String[] args) {
    List strings = new ArrayList();
    strings.add("Hello, World!");
    strings.add("Welcome to CodeWorld.");
    strings.add("This is an example");

    strings.add("Hello, World!");
    strings.add("Welcome to CodeWorld.");
    strings.add("This is an example");

    strings.add("Hello, World!");
    strings.add("Welcome to CodeWorld.");
    strings.add("This is an example");

    strings.add("Hello, World!");
    strings.add("Welcome to CodeWorld.");
    strings.add("This is an example");

    my_method(strings);
    for (Object string : strings) {
      System.out.println(string);
    }        
    
  }

Find below my solution.

  private static void my_method(List list){
    
	//Sort the list
    Object[] a = list.toArray();
    Arrays.sort(a);
    
    ListIterator i = list.listIterator();
    HashSet set = new HashSet<>();
    for (int j=0; j< list.size(); j++) {        
        if(!set.contains(a[j])){//Remove duplicate
          i.next();
          i.set(a[j]);
        }
        set.add(a[j]);
    }
    
    while(i.hasNext()){
      i.next();
      i.set(null);//Assign null to remaining values
    }
  }

Expected output

Hello, World!
This is an example
Welcome to CodeWorld.
null
null
null
null
null
null
null
null
null

Please feel free to add your suggestions/improvements to this.

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