我在heroku上设置了项目，并尝试将图片保存在c3中，但是出现了这个错误。
无法连接＆＃39; str＆＃39;和＆＃39; NoneType＆＃39;对象
我如何解决这个问题？
回溯：
File "/app/.heroku/python/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
111. response = callback(request, *callback_args, **callback_kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/contrib/admin/options.py" in wrapper
366. return self.admin_site.admin_view(view)(*args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
91. response = view_func(request, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
89. response = view_func(request, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/contrib/admin/sites.py" in inner
196. return view(request, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapper
25. return bound_func(*args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/utils/decorators.py" in _wrapped_view
91. response = view_func(request, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/utils/decorators.py" in bound_func
21. return func(self, *args2, **kwargs2)
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/transaction.py" in inner
209. return func(*args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/contrib/admin/options.py" in change_view
1054. self.save_model(request, new_object, form, True)
File "/app/.heroku/python/lib/python2.7/site-packages/django/contrib/admin/options.py" in save_model
709. obj.save()
File "/app/.heroku/python/lib/python2.7/site-packages/mptt/models.py" in save
717. super(MPTTModel, self).save(*args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/models/base.py" in save
463. self.save_base(using=using, force_insert=force_insert, force_update=force_update)
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/models/base.py" in save_base
527. values = [(f, None, (raw and getattr(self, f.attname) or f.pre_save(self, False))) for f in non_pks]
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/models/fields/files.py" in pre_save
249. file.save(file.name, file, save=False)
File "/app/.heroku/python/lib/python2.7/site-packages/easy_thumbnails/files.py" in save
605. **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/easy_thumbnails/files.py" in save
525. super(ThumbnailerFieldFile, self).save(name, content, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/models/fields/files.py" in save
85. name = self.field.generate_filename(self.instance, name)
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/models/fields/files.py" in generate_filename
263. return os.path.join(self.get_directory_name(), self.get_filename(filename))
File "/app/.heroku/python/lib/python2.7/site-packages/django/db/models/fields/files.py" in get_filename
260. return os.path.normpath(self.storage.get_valid_name(os.path.basename(filename)))
File "/app/.heroku/python/lib/python2.7/site-packages/queued_storage/backends.py" in get_valid_name
215. return self.get_storage(name).get_valid_name(name)
File "/app/.heroku/python/lib/python2.7/site-packages/queued_storage/backends.py" in get_storage
115. elif cache_result is None and self.remote.exists(name):
File "/app/.heroku/python/lib/python2.7/site-packages/storages/backends/s3boto.py" in exists
414. return k.exists()
File "/app/.heroku/python/lib/python2.7/site-packages/boto/s3/key.py" in exists
513. return bool(self.bucket.lookup(self.name))
File "/app/.heroku/python/lib/python2.7/site-packages/boto/s3/bucket.py" in lookup
141. return self.get_key(key_name, headers=headers)
File "/app/.heroku/python/lib/python2.7/site-packages/boto/s3/bucket.py" in get_key
169. key, resp = self._get_key_internal(key_name, headers, query_args_l)
File "/app/.heroku/python/lib/python2.7/site-packages/boto/s3/bucket.py" in _get_key_internal
176. query_args=query_args)
File "/app/.heroku/python/lib/python2.7/site-packages/boto/s3/connection.py" in make_request
535. auth_path = self.calling_format.build_auth_path(bucket, key)
File "/app/.heroku/python/lib/python2.7/site-packages/boto/s3/connection.py" in build_auth_path
93. path = '/' + bucket
Exception Type: TypeError at /admin/zakai/catalog/1/
Exception Value: cannot concatenate 'str' and 'NoneType' objects
Bucket and＆＃34; connection.py＆＃34;是空的