Program: 38908
Project: 38908
Buggy source:
private void updateSubstation(){
  if (substations == null) {
    LOGGER.trace("String_Node_Str");
    substations=new ArrayList<>();
    node2voltageLevel=new HashMap<>();
    UndirectedGraph<UcteNodeCode,Object> graph=createSubstationGraph(network);
    for (    Set<UcteNodeCode> substationNodes : new ConnectivityInspector<>(graph).connectedSets()) {
      UcteNodeCode mainNode=substationNodes.stream().sorted((nodeCode1,nodeCode2) -> {
        if (nodeCode1.getUcteCountryCode() == UcteCountryCode.XX && nodeCode2.getUcteCountryCode() != UcteCountryCode.XX) {
          return 1;
        }
 else         if (nodeCode1.getUcteCountryCode() != UcteCountryCode.XX && nodeCode2.getUcteCountryCode() == UcteCountryCode.XX) {
          return -1;
        }
 else {
          int c=Float.compare(nodeCode2.getVoltageLevelCode().getVoltageLevel(),nodeCode1.getVoltageLevelCode().getVoltageLevel());
          if (c == 0) {
            c=nodeCode2.getBusbar().compareTo(nodeCode1.getBusbar());
          }
          return c;
        }
      }
).findFirst().get();
      Multimap<UcteVoltageLevelCode,UcteNodeCode> nodesByVoltageLevel=Multimaps.index(substationNodes,nodeCode -> {
        return nodeCode.getVoltageLevelCode();
      }
);
      String substationName=mainNode.getUcteCountryCode().getUcteCode() + mainNode.getGeographicalSpot();
      List<UcteVoltageLevel> voltageLevels=new ArrayList<>();
      UcteSubstation substation=new UcteSubstation(substationName,voltageLevels);
      substations.add(substation);
      LOGGER.trace("String_Node_Str",substationName);
      for (      Map.Entry<UcteVoltageLevelCode,Collection<UcteNodeCode>> entry : nodesByVoltageLevel.asMap().entrySet()) {
        UcteVoltageLevelCode vlc=entry.getKey();
        Collection<UcteNodeCode> voltageLevelNodes=entry.getValue();
        String voltageLevelName=mainNode.getUcteCountryCode().getUcteCode() + mainNode.getGeographicalSpot() + vlc.ordinal();
        UcteVoltageLevel voltageLevel=new UcteVoltageLevel(voltageLevelName,substation,voltageLevelNodes);
        voltageLevels.add(voltageLevel);
        for (        UcteNodeCode voltageLevelNode : voltageLevelNodes) {
          node2voltageLevel.put(voltageLevelNode,voltageLevel);
        }
        LOGGER.trace("String_Node_Str",voltageLevelName,voltageLevelNodes);
      }
    }
  }
}

Fixed version (ground truth):
private void updateSubstation(){
  if (substations == null) {
    LOGGER.trace("String_Node_Str");
    substations=new ArrayList<>();
    node2voltageLevel=new HashMap<>();
    UndirectedGraph<UcteNodeCode,Object> graph=createSubstationGraph(network);
    for (    Set<UcteNodeCode> substationNodes : new ConnectivityInspector<>(graph).connectedSets()) {
      UcteNodeCode mainNode=substationNodes.stream().sorted((nodeCode1,nodeCode2) -> {
        if (nodeCode1.getUcteCountryCode() == UcteCountryCode.XX && nodeCode2.getUcteCountryCode() != UcteCountryCode.XX) {
          return 1;
        }
 else         if (nodeCode1.getUcteCountryCode() != UcteCountryCode.XX && nodeCode2.getUcteCountryCode() == UcteCountryCode.XX) {
          return -1;
        }
 else {
          int c=Float.compare(nodeCode2.getVoltageLevelCode().getVoltageLevel(),nodeCode1.getVoltageLevelCode().getVoltageLevel());
          if (c == 0) {
            c=nodeCode2.getBusbar().compareTo(nodeCode1.getBusbar());
          }
          return c;
        }
      }
).findFirst().orElseThrow(() -> new AssertionError());
      Multimap<UcteVoltageLevelCode,UcteNodeCode> nodesByVoltageLevel=Multimaps.index(substationNodes,UcteNodeCode::getVoltageLevelCode);
      String substationName=mainNode.getUcteCountryCode().getUcteCode() + mainNode.getGeographicalSpot();
      List<UcteVoltageLevel> voltageLevels=new ArrayList<>();
      UcteSubstation substation=new UcteSubstation(substationName,voltageLevels);
      substations.add(substation);
      LOGGER.trace("String_Node_Str",substationName);
      for (      Map.Entry<UcteVoltageLevelCode,Collection<UcteNodeCode>> entry : nodesByVoltageLevel.asMap().entrySet()) {
        UcteVoltageLevelCode vlc=entry.getKey();
        Collection<UcteNodeCode> voltageLevelNodes=entry.getValue();
        String voltageLevelName=mainNode.getUcteCountryCode().getUcteCode() + mainNode.getGeographicalSpot() + vlc.ordinal();
        UcteVoltageLevel voltageLevel=new UcteVoltageLevel(voltageLevelName,substation,voltageLevelNodes);
        voltageLevels.add(voltageLevel);
        for (        UcteNodeCode voltageLevelNode : voltageLevelNodes) {
          node2voltageLevel.put(voltageLevelNode,voltageLevel);
        }
        LOGGER.trace("String_Node_Str",voltageLevelName,voltageLevelNodes);
      }
    }
  }
}