old_contents: import os
  import tempfile
  from zipfile import ZipFile
  
  from django.dispatch import receiver
  from django.utils.translation import ugettext as _
  
  from ..exporter import BaseExporter
  from ..services.invoices import invoice_pdf_task
  from ..signals import register_data_exporters
  
  
  class InvoiceExporter(BaseExporter):
      identifier = 'invoices'
      verbose_name = _('All invoices')
  
      def render(self, form_data: dict):
          with tempfile.TemporaryDirectory() as d:
              with ZipFile(os.path.join(d, 'tmp.zip'), 'w') as zipf:
                  for i in self.event.invoices.all():
                      if not i.file:
                          invoice_pdf_task.apply_async(args=(i.pk))
                          i.refresh_from_db()
                      i.file.open('r')
                      zipf.writestr('{}.pdf'.format(i.number), i.file.read())
                      i.file.close()
  
              with open(os.path.join(d, 'tmp.zip'), 'rb') as zipf:
                  return 'invoices.zip', 'application/zip', zipf.read()
  
  
  @receiver(register_data_exporters, dispatch_uid="exporter_invoices")
  def register_invoice_export(sender, **kwargs):
      return InvoiceExporter
  
new_contents: import os
  import tempfile
  from zipfile import ZipFile
  
  from django.dispatch import receiver
  from django.utils.translation import ugettext as _
  
  from ..exporter import BaseExporter
  from ..services.invoices import invoice_pdf_task
  from ..signals import register_data_exporters
  
  
  class InvoiceExporter(BaseExporter):
      identifier = 'invoices'
      verbose_name = _('All invoices')
  
      def render(self, form_data: dict):
          with tempfile.TemporaryDirectory() as d:
              with ZipFile(os.path.join(d, 'tmp.zip'), 'w') as zipf:
                  for i in self.event.invoices.all():
                      if not i.file:
                          invoice_pdf_task.apply(args=(i.pk,))
                          i.refresh_from_db()
                      i.file.open('r')
                      zipf.writestr('{}.pdf'.format(i.number), i.file.read())
                      i.file.close()
  
              with open(os.path.join(d, 'tmp.zip'), 'rb') as zipf:
                  return 'invoices.zip', 'application/zip', zipf.read()
  
  
  @receiver(register_data_exporters, dispatch_uid="exporter_invoices")
  def register_invoice_export(sender, **kwargs):
      return InvoiceExporter
  
subject: Fix invalid task call