collectstatic -c fails since django 1.9 for s3 storage

[xblitz]

it seems that since django 1.9 specificaly this PR django/django@87d7824 it breaks the "collectstatic -c" since it tries to validate that the root directory exists (which is empty in out case) because the bucket.new_key fails if the key name is empty

In the case of django-storages, maybe we can check if the bucket exists or just return true if its empty? (I think I would go for the true if empty)

Here is the Traceback:

Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/app/.heroku/python/lib/python3.4/site-packages/django/core/management/__init__.py", line 353, in execute_from_command_line
    utility.execute()
  File "/app/.heroku/python/lib/python3.4/site-packages/django/core/management/__init__.py", line 345, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/app/.heroku/python/lib/python3.4/site-packages/django/core/management/base.py", line 348, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/app/.heroku/python/lib/python3.4/site-packages/django/core/management/base.py", line 399, in execute
    output = self.handle(*args, **options)
  File "/app/.heroku/python/lib/python3.4/site-packages/django/contrib/staticfiles/management/commands/collectstatic.py", line 176, in handle
    collected = self.collect()
  File "/app/.heroku/python/lib/python3.4/site-packages/django/contrib/staticfiles/management/commands/collectstatic.py", line 89, in collect
    self.clear_dir('')
  File "/app/.heroku/python/lib/python3.4/site-packages/django/contrib/staticfiles/management/commands/collectstatic.py", line 210, in clear_dir
    if not self.storage.exists(path):
  File "/app/.heroku/python/lib/python3.4/site-packages/storages/backends/s3boto.py", line 433, in exists
    k = self.bucket.new_key(self._encode_name(name))
  File "/app/.heroku/python/lib/python3.4/site-packages/boto/s3/bucket.py", line 622, in new_key
    raise ValueError('Empty key names are not allowed')
ValueError: Empty key names are not allowed

[jschneier]

Thanks for the report. I'm torn between the 2 possible fixes. From a strictly correctness standpoint I think that checking for bucket existence makes more sense. The only time that doesn't matter in this case is when you have set the setting AWS_AUTO_CREATE_BUCKET.

Side note: looks like we should be using get_key for checking existence.