title: cannot concatenate 'str' and 'NoneType' objects
body: <p>I set up the project on heroku and try to save the picture in the c3, but that's getting this error.</p>
  
  <blockquote>
    <p>cannot concatenate 'str' and 'NoneType' objects </p>
  </blockquote>
  
  <p>How i can fix that?</p>
  
  <p>Traceback:</p>
  
  <pre><code>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
  </code></pre>
  
  <p><strong>Bucket and "connection.py" is empty</strong></p>