output: #fixed code
                                  public List<String> tabComplete(CommandIssuer issuer, String commandLabel, String[] args) {
          return tabComplete(issuer, commandLabel, args, false);
      }
input: #vulnerable code 
                                  public List<String> tabComplete(CommandIssuer issuer, String commandLabel, String[] args)
          throws IllegalArgumentException {
  
          commandLabel = commandLabel.toLowerCase();
          try {
              CommandOperationContext commandOperationContext = preCommandOperation(issuer, commandLabel, args);
  
              final CommandSearch search = findSubCommand(args, true);
  
              String argString = ApacheCommonsLangUtil.join(args, " ").toLowerCase();
  
              final List<String> cmds = new ArrayList<>();
  
              if (search != null) {
                  cmds.addAll(completeCommand(commandOperationContext, issuer, search.cmd, Arrays.copyOfRange(args, search.argIndex, args.length), commandLabel));
              } else if (subCommands.get(UNKNOWN).size() == 1) {
                  cmds.addAll(completeCommand(commandOperationContext, issuer, Iterables.getOnlyElement(subCommands.get(UNKNOWN)), args, commandLabel));
              }
  
              for (Map.Entry<String, RegisteredCommand> entry : subCommands.entries()) {
                  final String key = entry.getKey();
                  if (key.startsWith(argString) && !UNKNOWN.equals(key) && !DEFAULT.equals(key)) {
                      final RegisteredCommand value = entry.getValue();
                      if (!value.hasPermission(issuer)) {
                          continue;
                      }
                      String prefCommand = value.prefSubCommand;
  
                      final String[] psplit = ACFPatterns.SPACE.split(prefCommand);
                      cmds.add(psplit[args.length - 1]);
                  }
              }
  
              return filterTabComplete(args[args.length - 1], cmds);
          } finally {
              postCommandOperation();
          }
      } 
                              #location 10 
                              #vulnerability type NULL_DEREFERENCE