char extractKey() {
            switch (type) {
                case PARAMETER:
                    return KEY_PARAMETER;
                case CATCH_ALL:
                    return KEY_CATCH_ALL;
                default:
                    return path.charAt(0);
            }
        }
Makes the given node as a child.
core/src/main/java/com/linecorp/armeria/server/RoutingTrieBuilder.java