Possible ConcurrentModificationException if Exec command fails

  public int run(List<String> command, List<String> output,
      List<String> errors) {
    int retCode = 1;
    ProcessBuilder pb = new ProcessBuilder(command);
    try {
      Process p = pb.start();
      OutputBufferThread stdOut = new OutputBufferThread(p.getInputStream());
      OutputBufferThread stdErr = new OutputBufferThread(p.getErrorStream());
      stdOut.start();
      stdErr.start();
      retCode = p.waitFor();
      if (retCode != 0) {
        mojo.getLog().warn(command + " failed with error code " + retCode);
        for (String s : stdErr.getOutput()) {
          mojo.getLog().debug(s);
        }
      }
      stdOut.join();
      stdErr.join();