old_contents: from objtrack.models import ObjectTracker
  
  try:
      from coffin import template
  except ImportError:
      from django import template
  
  register = template.Library()
  
  @register.filter()
  def with_tracking(queryset, session, date_field):
      tracker = ObjectTracker(session)
      for obj in queryset:
          yield obj, tracker.has_viewed(obj, date_field)
new_contents: from objtrack.models import ObjectTracker
  
  try:
      from coffin import template
  except ImportError:
      from django import template
  
  register = template.Library()
  
  @register.filter()
  def with_tracking(queryset, session, date_field=None):
      tracker = ObjectTracker(session)
      for obj in queryset:
          yield obj, tracker.has_viewed(obj, date_field)
subject: Make date_field optional