Program: 88496
Project: 88496
Buggy source:
public static BiFunction<String,Project,Element> getIdToElementConverter(){
  if (ID_TO_ELEMENT_CONVERTER == null) {
    ID_TO_ELEMENT_CONVERTER=(id,project) -> {
      if (id == null) {
        return null;
      }
      if (id.equals(project.getID()) || id.equals(project.getPrimaryProject().getProjectID())) {
        return null;
      }
      BaseElement baseElement=project.getElementByID(id);
      if (baseElement == null) {
        return null;
      }
      if (id.endsWith(MDKConstants.PRIMARY_MODEL_ID_SUFFIX)) {
        String projectId=id.substring(0,id.length() - MDKConstants.PRIMARY_MODEL_ID_SUFFIX.length());
        if (projectId.equals(Converters.getIProjectToIdConverter().apply(project.getPrimaryProject()))) {
          return project.getPrimaryModel();
        }
      }
      if (id.endsWith(MDKConstants.APPLIED_STEREOTYPE_INSTANCE_ID_SUFFIX)) {
        String stereotypedElementId=id.substring(0,id.length() - MDKConstants.APPLIED_STEREOTYPE_INSTANCE_ID_SUFFIX.length());
        Element stereotypedElement=ID_TO_ELEMENT_CONVERTER.apply(stereotypedElementId,project);
        if (stereotypedElement != null) {
          return stereotypedElement.getAppliedStereotypeInstance();
        }
      }
      if (id.contains(MDKConstants.SLOT_VALUE_ID_SEPARATOR)) {
        String[] sections=id.split(MDKConstants.SLOT_VALUE_ID_SEPARATOR);
        Element element=Converters.getIdToElementConverter().apply(sections[0],project);
        if (element == null || !(element instanceof Slot)) {
          return null;
        }
        Slot owningSlot=(Slot)element;
        String[] subSections=sections[1].split("String_Node_Str");
        if (subSections.length != 2) {
          return null;
        }
        if (!NumberUtils.isDigits(subSections[0])) {
          return null;
        }
        int index;
        try {
          index=Integer.parseInt(subSections[0]);
        }
 catch (        NumberFormatException ignored) {
          return null;
        }
        if (index < 0 || index >= owningSlot.getValue().size()) {
          return null;
        }
        ValueSpecification value=owningSlot.getValue().get(index);
        if (!value.eClass().getName().toLowerCase().equals(subSections[1])) {
          return null;
        }
        return value;
      }
      if (id.contains(MDKConstants.SLOT_ID_SEPARATOR) && !id.contains(MDKConstants.SLOT_VALUE_ID_SEPARATOR)) {
        String[] sections=id.split(MDKConstants.SLOT_ID_SEPARATOR);
        Element owningInstance=Converters.getIdToElementConverter().apply(sections[0],project);
        Element definingFeature=Converters.getIdToElementConverter().apply(sections[1],project);
        if (!(owningInstance instanceof InstanceSpecification) || !(definingFeature instanceof StructuralFeature)) {
          return null;
        }
        return ((InstanceSpecification)owningInstance).getSlot().stream().filter(slot -> definingFeature.equals(slot.getDefiningFeature())).findAny().orElse(null);
      }
      return baseElement instanceof Element ? (Element)baseElement : null;
    }
;
  }
  return ID_TO_ELEMENT_CONVERTER;
}

Fixed version (ground truth):
public static BiFunction<String,Project,Element> getIdToElementConverter(){
  if (ID_TO_ELEMENT_CONVERTER == null) {
    ID_TO_ELEMENT_CONVERTER=(id,project) -> {
      if (id == null) {
        return null;
      }
      if (id.equals(project.getID()) || id.equals(project.getPrimaryProject().getProjectID())) {
        return null;
      }
      BaseElement baseElement=project.getElementByID(id);
      if (baseElement instanceof Element) {
        return (Element)baseElement;
      }
      if (id.endsWith(MDKConstants.PRIMARY_MODEL_ID_SUFFIX)) {
        String projectId=id.substring(0,id.length() - MDKConstants.PRIMARY_MODEL_ID_SUFFIX.length());
        if (projectId.equals(Converters.getIProjectToIdConverter().apply(project.getPrimaryProject()))) {
          return project.getPrimaryModel();
        }
      }
      if (id.endsWith(MDKConstants.APPLIED_STEREOTYPE_INSTANCE_ID_SUFFIX)) {
        String stereotypedElementId=id.substring(0,id.length() - MDKConstants.APPLIED_STEREOTYPE_INSTANCE_ID_SUFFIX.length());
        Element stereotypedElement=ID_TO_ELEMENT_CONVERTER.apply(stereotypedElementId,project);
        if (stereotypedElement != null) {
          return stereotypedElement.getAppliedStereotypeInstance();
        }
      }
      if (id.contains(MDKConstants.SLOT_VALUE_ID_SEPARATOR)) {
        String[] sections=id.split(MDKConstants.SLOT_VALUE_ID_SEPARATOR);
        Element element=Converters.getIdToElementConverter().apply(sections[0],project);
        if (element == null || !(element instanceof Slot)) {
          return null;
        }
        Slot owningSlot=(Slot)element;
        String[] subSections=sections[1].split("String_Node_Str");
        if (subSections.length != 2) {
          return null;
        }
        if (!NumberUtils.isDigits(subSections[0])) {
          return null;
        }
        int index;
        try {
          index=Integer.parseInt(subSections[0]);
        }
 catch (        NumberFormatException ignored) {
          return null;
        }
        if (index < 0 || index >= owningSlot.getValue().size()) {
          return null;
        }
        ValueSpecification value=owningSlot.getValue().get(index);
        if (!value.eClass().getName().toLowerCase().equals(subSections[1])) {
          return null;
        }
        return value;
      }
      if (id.contains(MDKConstants.SLOT_ID_SEPARATOR) && !id.contains(MDKConstants.SLOT_VALUE_ID_SEPARATOR)) {
        String[] sections=id.split(MDKConstants.SLOT_ID_SEPARATOR);
        Element owningInstance=Converters.getIdToElementConverter().apply(sections[0],project);
        Element definingFeature=Converters.getIdToElementConverter().apply(sections[1],project);
        if (!(owningInstance instanceof InstanceSpecification) || !(definingFeature instanceof StructuralFeature)) {
          return null;
        }
        return ((InstanceSpecification)owningInstance).getSlot().stream().filter(slot -> definingFeature.equals(slot.getDefiningFeature())).findAny().orElse(null);
      }
      return null;
    }
;
  }
  return ID_TO_ELEMENT_CONVERTER;
}