Map<String, List<String>> metaData = new HashMap<String, List<String>>();
List<String> res = new ArrayList<String>();
res.add("karan");
metaData.computeIfAbsent("ih",  k -> new ArrayList<String>()).addAll(res);
List<String> res2 = new ArrayList<String>();
res.add("karan222");
metaData.computeIfAbsent("ih",  k -> new ArrayList<String>()).addAll(res2);
System.out.println(metaData);