/**
     * Indicates to the server that a client side interceptor is interested in the context data that is stored
     * under the given key. Any object on the context data map (i.e. {@code InvocationContext.getContextData()} that is
     * present at the end of the server invocation will be serialised and returned to the client.
     *
     * If an object is present under this key and is not serializable then the request will fail.
     *
     * @param key The context data key the client interceptor is interested in
     */
    public void addReturnedContextDataKey(String key) {
        Object returnedData = getContextData().get(RETURNED_CONTEXT_DATA_KEY);
        if(returnedData == null) {
            getContextData().put(RETURNED_CONTEXT_DATA_KEY, returnedData = new HashSet<>());
        } else if(!(returnedData instanceof Set)) {
            throw Logs.INVOCATION.returnedContextDataKeyOfWrongType();
        }
        Set<String> keys = (Set<String>) returnedData;
        keys.add(key);
    }