How to work with nested ArrayList in HashMap?

Question

Java

For example I have:

HashMap<Integer, ArrayList<String>> containerA = new HashMap<Integer, ArrayList<String>>();
Integer ea = 11;

How to add an element to an ArrayList by key? If, for example, you do this: then if there is no such key, then there will be an error.
containerA.put(ea, add("LOL"));//будет ошибка
containerA.get(ea).add("LOL");