#vulnerable code 
                                private void handleMyHandshakeMessage(HandshakeMessage handshakeMessage) throws IOException {
        ProtocolMessageHandler pmh = null;// TODO//handshakeMessage.getProtocolMessageHandler(tlsContext);
        handshakeMessage.setMessageSeq(sendHandshakeMessageSeq);
        byte[] handshakeMessageBytes = pmh.prepareMessage(previousMessage);

        handshakeMessageSendBuffer = ArrayConverter.concatenate(handshakeMessageSendBuffer,
                handshakeFragmentHandler.fragmentHandshakeMessage(handshakeMessageBytes, maxPacketSize - 25));

        retransmitList.add(handshakeMessageSendBuffer);

        if (handshakeMessageSendRecordList == null) {
            handshakeMessageSendRecordList = new ArrayList<>();
            handshakeMessageSendRecordList.add(new DtlsRecord());
        }

        handshakeMessage.setRecords(handshakeMessageSendRecordList);

        bufferSendData(recordHandler.wrapData(handshakeMessageSendBuffer, ProtocolMessageType.HANDSHAKE,
                handshakeMessage.getRecords()));

        sendHandshakeMessageSeq++;
    } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private void handleMyHandshakeMessage(HandshakeMessage handshakeMessage) throws IOException {
        HandshakeMessageHandler pmh = (HandshakeMessageHandler) handshakeMessage.getHandler(tlsContext);
        byte[] handshakeMessageBytes = pmh.prepareMessage(handshakeMessage);

        handshakeMessageSendBuffer = ArrayConverter.concatenate(handshakeMessageSendBuffer,
                handshakeFragmentHandler.fragmentHandshakeMessage(handshakeMessageBytes, maxPacketSize - 25));

        retransmitList.add(handshakeMessageSendBuffer);

        if (handshakeMessageSendRecordList == null) {
            handshakeMessageSendRecordList = new ArrayList<>();
            handshakeMessageSendRecordList.add(new DtlsRecord());
        }

        handshakeMessage.setRecords(handshakeMessageSendRecordList);

        bufferSendData(recordHandler.wrapData(handshakeMessageSendBuffer, ProtocolMessageType.HANDSHAKE,
                handshakeMessage.getRecords()));

        tlsContext.setSequenceNumber(tlsContext.getSequenceNumber() + 1);
    }