Implementation of the isAnagram problem and groupAnagrams

Anagrams.java

import java.util.*;
class Main {
  public static void main(String[] args) {
    List<String> words = new ArrayList<>(Arrays.asList("a", "b", "a", "d"));
    List<List<String>> g = groupAnamgrams(words);
    System.out.println(g);
  }
  
  public static List<List<String>> groupAnamgrams(List<String> anagrams){
    if (anagrams == null || anagrams.isEmpty()) {
      return new ArrayList<List<String>>();
    }
    
    Map<String, List<String>> map = new HashMap<>();
    for (String s : anagrams) {
      String key = sort(s);
      if (map.containsKey(key)) {
        map.get(key).add(key);
      } else {
        List<String> listOfSameAnagrams = new ArrayList<String>();
        listOfSameAnagrams.add(key);
        map.put(key, listOfSameAnagrams);
      }
    }
    
    List<List<String>> groups = new ArrayList<>();
    for(Map.Entry<String, List<String>> entry : map.entrySet()) {
      groups.add(entry.getValue());
    }
    return groups;
  }
  
  public static boolean isAnagram(String s1, String s2) {
    if (s1 == null && s2 == null) {
      return true;
    }
    
    if (s1 == null && s2 != null) {
      return false;
    }
    
    if (s2 == null && s1 != null) {
      return false;
    }
    
    return sort(s1).equals(sort(s2));
  }
  
  public static String sort(String unsortedString) {
    char[] cha = unsortedString.toCharArray();
    // in place sorting
    Arrays.sort(cha);
    return new String(cha);
  }
}