output: #fixed code
                                  public void startTlsServer(TlsConfig config) {
          TlsContext tlsContext = new TlsContext(config);
          WorkflowExecutor workflowExecutor = WorkflowExecutorFactory.createWorkflowExecutor(config.getExecutorType(),
                  tlsContext);
          try {
              workflowExecutor.executeWorkflow();
          } catch (WorkflowExecutionException ex) {
              LOGGER.info("The TLS protocol flow was not executed completely, follow the debug messages for more information.");
              LOGGER.debug(ex.getLocalizedMessage(), ex);
          }
      }
input: #vulnerable code 
                                  public void startTlsServer(TlsConfig config) {
          TlsContext tlsContext = new TlsContext(config);
          WorkflowExecutor workflowExecutor = WorkflowExecutorFactory.createWorkflowExecutor(config.getExecutorType(),
                  tlsContext);
          try {
              workflowExecutor.executeWorkflow();
          } catch (WorkflowExecutionException ex) {
              LOGGER.info("The TLS protocol flow was not executed completely, follow the debug messages for more information.");
              LOGGER.debug(ex.getLocalizedMessage(), ex);
          }
  
          if (config.getWorkflowOutput() != null && !config.getWorkflowOutput().isEmpty()) {
              FileOutputStream fos = null;
              try {
                  fos = new FileOutputStream(config.getWorkflowOutput());
                  WorkflowTraceSerializer.write(fos, tlsContext.getWorkflowTrace());
              } catch (JAXBException | IOException ex) {
                  LOGGER.info("Could not serialize WorkflowTrace.");
                  LOGGER.debug(ex);
              } finally {
                  try {
                      fos.close();
                  } catch (IOException ex) {
                      LOGGER.info("Could not serialize WorkflowTrace.");
                      LOGGER.debug(ex);
                  }
              }
          }
      } 
                              #location 22 
                              #vulnerability type NULL_DEREFERENCE