Program: 88530
Project: 88530
Buggy source:
static PreProcessor getCreatePreProcessor(BiFunction<String,Project,Element> idToElementConverter){
  return new PreProcessor((objectNode,project,strict,element) -> {
    if (element != null) {
      return element;
    }
    JsonNode jsonNode=objectNode.get(MDKConstants.TYPE_KEY);
    if (jsonNode == null || !jsonNode.isTextual()) {
      return null;
    }
    String type=jsonNode.asText();
    if (type.equals(UMLPackage.Literals.DIAGRAM.getName())) {
      JsonNode diagramTypeJsonNode=objectNode.get(MDKConstants.DIAGRAM_TYPE_KEY);
      if (diagramTypeJsonNode == null || !diagramTypeJsonNode.isTextual()) {
        return null;
      }
      JsonNode ownerJsonNode=objectNode.get(MDKConstants.OWNER_ID_KEY);
      if (ownerJsonNode == null || !ownerJsonNode.isTextual()) {
        return null;
      }
      Element owner=idToElementConverter.apply(ownerJsonNode.asText(),project);
      if (owner == null || !(owner instanceof Namespace)) {
        return null;
      }
      try {
        return ModelElementsManager.getInstance().createDiagram(diagramTypeJsonNode.asText(),(Namespace)owner);
      }
 catch (      ReadOnlyElementException e) {
        throw new ImportException(element,objectNode,e.getMessage(),e);
      }
    }
    EClassifier eClassifier=UMLPackage.eINSTANCE.getEClassifier(type);
    if (!(eClassifier instanceof EClass)) {
      return null;
    }
    EObject eObject=UMLFactory.eINSTANCE.create((EClass)eClassifier);
    if (!(eObject instanceof Element)) {
      return null;
    }
    return (Element)eObject;
  }
);
}

Fixed version (ground truth):
static PreProcessor getCreatePreProcessor(BiFunction<String,Project,Element> idToElementConverter){
  return new PreProcessor((objectNode,project,strict,element) -> {
    if (element != null) {
      return element;
    }
    JsonNode jsonNode=objectNode.get(MDKConstants.TYPE_KEY);
    if (jsonNode == null || !jsonNode.isTextual()) {
      return null;
    }
    String type=jsonNode.asText();
    if (type.equals(UMLPackage.Literals.DIAGRAM.getName())) {
      JsonNode diagramTypeJsonNode=objectNode.get(MDKConstants.DIAGRAM_TYPE_KEY);
      if (diagramTypeJsonNode == null || !diagramTypeJsonNode.isTextual()) {
        return null;
      }
      JsonNode ownerJsonNode=objectNode.get(MDKConstants.OWNER_ID_KEY);
      if (ownerJsonNode == null || !ownerJsonNode.isTextual()) {
        return null;
      }
      Element owner=idToElementConverter.apply(ownerJsonNode.asText(),project);
      if (owner == null || !(owner instanceof Namespace)) {
        return null;
      }
      try {
        return ModelElementsManager.getInstance().createDiagram(diagramTypeJsonNode.asText(),(Namespace)owner);
      }
 catch (      ReadOnlyElementException e) {
        throw new ImportException(element,objectNode,e.getMessage(),e);
      }
    }
    EClassifier eClassifier=UMLPackage.eINSTANCE.getEClassifier(type);
    if (!(eClassifier instanceof EClass)) {
      return null;
    }
    AbstractRepository initialRepository=(UMLFactory.eINSTANCE instanceof UMLFactoryImpl) ? ((UMLFactoryImpl)UMLFactory.eINSTANCE).getRepository() : null;
    UMLFactory.eINSTANCE.setRepository(project.getRepository());
    EObject eObject=UMLFactory.eINSTANCE.create((EClass)eClassifier);
    UMLFactory.eINSTANCE.setRepository(initialRepository);
    if (!(eObject instanceof Element)) {
      return null;
    }
    return (Element)eObject;
  }
);
}