I can't connect a Socket to another device - cannot evaluate StructAddrinfo.toString()

Question

I'm trying to move a Java project I've made and tested to Android. My problem appears when I create the Socket with the Strings for the IP and port (which are not null and correspond to the IP of an open and working server). A NullPointerException appears. The code is an AsyncTask that is activated when the user presses a button. This is the doInBackground method:

@Override
protected Void doInBackground(String... strings) {
    client = new Client(strings[0]);
    DataStorage.getInstance().setClient(client);

    try {
        boolean a = client.connectToServer(strings[0]); //It dies here
        if (!(un).equals("")&&a) {
            Toast.makeText(context,"Connected",Toast.LENGTH_SHORT).show();

            Intent intent = new Intent(context, AvailableClientsActivity.class);
            context.startActivity(intent);

        } else {
            Toast.makeText(context,"Username invalid",Toast.LENGTH_SHORT).show();
        }
    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (IOException e) {
        client.resetConnection();
    }

    return null;
}

This is the message I get Method threw 'java.lang.NullPointerException' exception. Cannot evalueate android.system.StructAddrinfo.toString()

I've just started with Android so it might be something basic I've skipped.