core/src/main/java/net/typedrest/AbstractEndpoint.java
private static Map<URI, String> getOrAdd(Map<String, Map<URI, String>> map, String key) {
        Map<URI, String> value = map.get(key);
        if (value == null) {
            map.put(key, value = new HashMap<>());
        }
        return value;
    }
private static Map<URI, String> getOrAdd(Map<String, Map<URI, String>> map, String key) {
        Map<URI, String> value = map.get(key);
        if (value == null) {
            map.put(key, value = new HashMap<>());
        }
        return value;
    }
Returns the element with the specified key from the map. Creates, adds
and returns a new element if no match was found.

@param map The map to look in.
@param key The key to look for.
@return The existing or new element.