Program: 86190
Project: 86190
Buggy source:
@Override public ReservationResult reservation(DetailledItem item,Account acc,int useraction,String selection) throws IOException {
  if (System.currentTimeMillis() - logged_in > SESSION_LIFETIME || logged_in_as == null) {
    try {
      login(acc);
    }
 catch (    OpacErrorException e) {
      return new ReservationResult(MultiStepResult.Status.ERROR,e.getMessage());
    }
  }
 else   if (logged_in_as.getId() != acc.getId()) {
    try {
      login(acc);
    }
 catch (    OpacErrorException e) {
      return new ReservationResult(MultiStepResult.Status.ERROR,e.getMessage());
    }
  }
  String html;
  if (reusehtml_reservation != null) {
    html=reusehtml_reservation;
  }
 else {
    html=httpGet(item.getReservation_info(),ENCODING);
  }
  Document doc=Jsoup.parse(html);
  if (doc.select("String_Node_Str").size() > 0) {
    return new ReservationResult(MultiStepResult.Status.ERROR,doc.select("String_Node_Str").first().text());
  }
  List<NameValuePair> nameValuePairs=new ArrayList<>();
  nameValuePairs.add(new BasicNameValuePair("String_Node_Str","String_Node_Str"));
  if (doc.select("String_Node_Str").size() > 0) {
    nameValuePairs.add(new BasicNameValuePair("String_Node_Str",doc.select("String_Node_Str").val()));
  }
  if (doc.select("String_Node_Str").size() > 0 && selection == null) {
    Elements options=doc.select("String_Node_Str");
    ReservationResult res=new ReservationResult(MultiStepResult.Status.SELECTION_NEEDED);
    List<Map<String,String>> optionsMap=new ArrayList<>();
    for (    Element option : options) {
      Map<String,String> selopt=new HashMap<>();
      selopt.put("String_Node_Str",option.attr("String_Node_Str"));
      selopt.put("String_Node_Str",option.text());
      optionsMap.add(selopt);
    }
    res.setSelection(optionsMap);
    res.setMessage(doc.select("String_Node_Str").text());
    reusehtml_reservation=html;
    return res;
  }
 else   if (selection != null) {
    nameValuePairs.add(new BasicNameValuePair("String_Node_Str",selection));
    reusehtml_reservation=null;
  }
  html=httpPost(opac_url + "String_Node_Str",new UrlEncodedFormEntity(nameValuePairs),ENCODING);
  doc=Jsoup.parse(html);
  if (doc.select("String_Node_Str").size() > 0) {
    return new ReservationResult(MultiStepResult.Status.OK);
  }
 else   if (doc.select("String_Node_Str").size() > 0) {
    return new ReservationResult(MultiStepResult.Status.ERROR,doc.select("String_Node_Str").text());
  }
 else {
    return new ReservationResult(MultiStepResult.Status.ERROR);
  }
}

Fixed version (ground truth):
@Override public ReservationResult reservation(DetailledItem item,Account acc,int useraction,String selection) throws IOException {
  try {
    login(acc);
  }
 catch (  OpacErrorException e) {
    return new ReservationResult(MultiStepResult.Status.ERROR,e.getMessage());
  }
  String html;
  if (reusehtml_reservation != null) {
    html=reusehtml_reservation;
  }
 else {
    html=httpGet(item.getReservation_info(),ENCODING);
  }
  Document doc=Jsoup.parse(html);
  if (doc.select("String_Node_Str").size() > 0) {
    return new ReservationResult(MultiStepResult.Status.ERROR,doc.select("String_Node_Str").first().text());
  }
  List<NameValuePair> nameValuePairs=new ArrayList<>();
  nameValuePairs.add(new BasicNameValuePair("String_Node_Str","String_Node_Str"));
  if (doc.select("String_Node_Str").size() > 0) {
    nameValuePairs.add(new BasicNameValuePair("String_Node_Str",doc.select("String_Node_Str").val()));
  }
  if (doc.select("String_Node_Str").size() > 0 && selection == null) {
    Elements options=doc.select("String_Node_Str");
    ReservationResult res=new ReservationResult(MultiStepResult.Status.SELECTION_NEEDED);
    List<Map<String,String>> optionsMap=new ArrayList<>();
    for (    Element option : options) {
      Map<String,String> selopt=new HashMap<>();
      selopt.put("String_Node_Str",option.attr("String_Node_Str"));
      selopt.put("String_Node_Str",option.text());
      optionsMap.add(selopt);
    }
    res.setSelection(optionsMap);
    res.setMessage(doc.select("String_Node_Str").text());
    reusehtml_reservation=html;
    return res;
  }
 else   if (selection != null) {
    nameValuePairs.add(new BasicNameValuePair("String_Node_Str",selection));
    reusehtml_reservation=null;
  }
  nameValuePairs.add(new BasicNameValuePair("String_Node_Str","String_Node_Str"));
  html=httpPost(opac_url + "String_Node_Str",new UrlEncodedFormEntity(nameValuePairs),ENCODING);
  doc=Jsoup.parse(html);
  if (doc.select("String_Node_Str").size() > 0) {
    return new ReservationResult(MultiStepResult.Status.OK);
  }
 else   if (doc.select("String_Node_Str").size() > 0) {
    return new ReservationResult(MultiStepResult.Status.ERROR,doc.select("String_Node_Str").text());
  }
 else {
    return new ReservationResult(MultiStepResult.Status.ERROR);
  }
}