Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException; Error in the translation of an OID in the snmp management entity.

What happens is that when I try to translate the information in the form of Response Event to String I get an exception, I think it's in this method, maybe I'm ignoring something, it's a new class for me, so I do not know it very well; this is the code of the methods that eclipse shows me:

//metodo traducir


public String traducirOid (OID oid) throws IOException 
{
    ResponseEvent event = obtenerOID(new OID[] { oid });
    return event.getResponse().get(0).getVariable().toString();
}

and

    public void actionPerformed(ActionEvent e) 
        {
            try
            {
                segmentosIN = principal.traducirOid(new OID(principal.OIDin));



                segmentosOUT = principal.traducirOid(new OID(principal.OIDout));

                cuadrotexto.append("segmentos recibidos: " + segmentosIN + "\n" + "segmentos enviados: " + segmentosOUT);
            } catch (IOException e1) {

                e1.printStackTrace();
            }

These are the other methods implemented:

public ResponseEvent obtenerOID(OID oids[]) throws IOException
{
    PDU pdu = new PDU();
    for (OID oid : oids) {
        pdu.add(new VariableBinding(oid));
    }

    pdu.setType(PDU.GET);
    ResponseEvent event = snmp.send(pdu, ObtenerTarget(), null);
    if(event != null) {
        return event;
    }
    throw new RuntimeException("GET timed out");
}

private Target ObtenerTarget() {
    Address targetAddress = GenericAddress.parse(address);
    CommunityTarget target = new CommunityTarget();
    target.setCommunity(new OctetString("Redes20182-ganadores"));
    target.setAddress(targetAddress);
    target.setRetries(2);
    target.setTimeout(1500);
    target.setVersion(SnmpConstants.version2c);
    return target;
}

I'm trying to translate an OID that shows me the TCP segments sent and received every so often ...

I hope you can help me. Greetings and thanks anything.