private <T> void update(Map<String, T> map, String key, T value) {
        if (key != null) {
            map.put(key, value);
        }
    }
Return the content of the mapping as an array with all specifications as given

@return port mappings as JSON array or null if no mappings exist
src/main/java/io/fabric8/maven/docker/access/PortMapping.java