output: #fixed code
                                  public static void start(List<GraphvizEngine> engines) throws IOException {
          final String executable = SystemUtils.executableName("java");
          final List<String> cmd = new ArrayList<>(Arrays.asList(
                  System.getProperty("java.home") + "/bin/" + executable,
                  "-cp", System.getProperty("java.class.path"), GraphvizServer.class.getName()));
          cmd.addAll(engines.stream().map(e -> e.getClass().getName()).collect(toList()));
          new ProcessBuilder(cmd).inheritIO().start();
      }
input: #vulnerable code 
                                  public static void start(List<GraphvizEngine> engines) throws IOException {
          final boolean windows = System.getProperty("os.name").contains("windows");
          final String executable = windows ? "java.exe" : "java";
          final List<String> cmd = new ArrayList<>(Arrays.asList(
                  System.getProperty("java.home") + "/bin/" + executable,
                  "-cp", System.getProperty("java.class.path"), GraphvizServer.class.getName()));
          cmd.addAll(engines.stream().map(e -> e.getClass().getName()).collect(toList()));
          new ProcessBuilder(cmd).inheritIO().start();
      } 
                              #location 2 
                              #vulnerability type NULL_DEREFERENCE