src/main/java/com/workplacesystems/utilsj/collections/TransactionalHashMap.java
@SuppressWarnings("unchecked")
    static <T> T maskNull(T key)
    {
        return (key == null ? (T)NULL_KEY : key);
    }
@SuppressWarnings("unchecked")
    static <T> T maskNull(T key)
    {
        return (key == null ? (T)NULL_KEY : key);
    }
Returns internal representation for key. Use NULL_KEY if key is null.