#vulnerable code 
                                private String newTransactionUrl() {

        String url = transactionEndpoint(driverConfig.getURI());
        LOGGER.debug( "Thread {}: POST {}", Thread.currentThread().getId(), url );

        try (CloseableHttpResponse response = executeHttpRequest(new HttpPost(url))) {
            Header location = response.getHeaders("Location")[0];
            response.close();
            return location.getValue();
        } catch (Exception e) {
            throw new ResultProcessingException("Could not obtain new Transaction: ", e);
        }
    } 
                            #location 7 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                private String newTransactionUrl() {

        String url = transactionEndpoint(driverConfig.getURI());
        LOGGER.debug( "Thread: {}, POST {}", Thread.currentThread().getId(), url );

        HttpPost request = new HttpPost(url);

        try (CloseableHttpResponse response = executeHttpRequest(request)) {
            Header location = response.getHeaders("Location")[0];
            return location.getValue();
        } catch (IOException ioe) {
            throw new HttpRequestException(request, ioe);
        }

    }