old_contents: from website.project.taxonomies import Subject
  from admin.nodes.serializers import serialize_node
  
  
  def serialize_preprint(preprint):
  
      return {
          'id': preprint._id,
          'date_created': preprint.date_created,
          'modified': preprint.date_modified,
          'provider': preprint.provider,
          'node': serialize_node(preprint.node),
          'is_published': preprint.is_published,
          'date_published': preprint.date_published,
          'subjects': serialize_subjects(preprint.subject_hierarchy),
      }
  
  
  def serialize_subjects(subject_hierarchy):
      return [{'id': subject._id, 'text': subject.text} for subjects in subject_hierarchy for subject in subjects]
  
new_contents: from admin.nodes.serializers import serialize_node
  
  
  def serialize_preprint(preprint):
  
      return {
          'id': preprint._id,
          'date_created': preprint.date_created,
          'modified': preprint.date_modified,
          'provider': preprint.provider,
          'node': serialize_node(preprint.node),
          'is_published': preprint.is_published,
          'date_published': preprint.date_published,
          'subjects': serialize_subjects(preprint.subject_hierarchy),
      }
  
  
  def serialize_subjects(subject_hierarchy):
      return [{'id': subject._id, 'text': subject.text} for subjects in subject_hierarchy for subject in subjects]
  
subject: Remove old import