new_contents: from django.db import migrations, models
  from django.db.models import Count
  
  
  def forwards(apps, schema_editor):
      Course = apps.get_model("catalog", "Course")
      empty_orphans = Course.objects.annotate(
          docs=Count("document", distinct=True), cats=Count("categories", distinct=True)
      ).filter(docs=0, cats=0)
      empty_orphans.delete()
  
  
  class Migration(migrations.Migration):
      dependencies = [
          ("catalog", "0016_alter_category_type_courseuserview"),
      ]
  
      operations = [
          migrations.RunSQL(sql="DROP TABLE IF EXISTS telepathy_message"),
          migrations.RunSQL(sql="DROP TABLE IF EXISTS telepathy_thread"),
          migrations.RunPython(forwards, migrations.RunPython.noop),
      ]
  
subject: Remove empty orphans while migrating