@Nullable
    public ServerPort activePort() {
        return activePort0(null);
    }
Returns the primary {@link ServerPort} that this {@link Server} is listening to. If this {@link Server}
has both a local port and a non-local port, the non-local port is returned.

@return the primary {@link ServerPort}, or {@code null} if this {@link Server} did not start.
core/src/main/java/com/linecorp/armeria/server/Server.java