Download of multiple files or folder raises server error: AttributeError: 'SeafileAPI' object has no attribute 'is_dir_downloadable'

When I try to download multiple files via the web interface I get a server error. I’m using seafile-server-7.1.4 and seahub-7.1.6, communty edition on FreeBSD (installed via pkg), sqlite. Everything else works fine. Any ideas? This was in the seahub log:

2020-09-16 04:23:40,431 [ERROR] django.request:135 handle_uncaught_exception Internal Server Error: /api/v2.1/repos/cf083a2e-d185-419e-ac8f-47c7bd9701e0/zip-task/
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/exception.py", line 41, in inner
response = get_response(request)
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/base.py", line 249, in _legacy_get_response
response = self._get_response(request)
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/base.py", line 187, in _get_response
response = self.process_exception_by_middleware(e, request)
  File "/usr/local/lib/python3.7/site-packages/django/core/handlers/base.py", line 185, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/local/lib/python3.7/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
return view_func(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/django/views/generic/base.py", line 68, in view
return self.dispatch(request, *args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/rest_framework/views.py", line 505, in dispatch
response = self.handle_exception(exc)
  File "/usr/local/lib/python3.7/site-packages/rest_framework/views.py", line 465, in handle_exception
self.raise_uncaught_exception(exc)
  File "/usr/local/lib/python3.7/site-packages/rest_framework/views.py", line 476, in raise_uncaught_exception
raise exc
  File "/usr/local/lib/python3.7/site-packages/rest_framework/views.py", line 502, in dispatch
response = handler(request, *args, **kwargs)
  File "/usr/local/www/haiwen/seafile-server/seahub/seahub/api2/endpoints/zip_task.py", line 267, in post
if not json.loads(seafile_api.is_dir_downloadable(repo_id, json.dumps(full_dirent_path_list), \
AttributeError: 'SeafileAPI' object has no attribute 'is_dir_downloadable'