UnboundLocalError on S3Bucket.listdir() method

[dahlia]

S3Bucket.listdir() method raises UnboundLocalError. It seems to occur when its result list is empty, but I have no idea about its detail. What is next_marker attribute for?

Traceback (most recent call last):
  File "/.../app.py", line 134, in list_sizes
    keys = list(self.bucket.listdir(prefix=prefix + '/'))
  File "/home/styleshare/lib/python2.7/site-packages/simples3/bucket.py", line 395, in listdir
    for item in listing:
  File "/home/styleshare/lib/python2.7/site-packages/simples3/bucket.py", line 189, in __iter__
    self.next_marker = item[0]
UnboundLocalError: local variable 'item' referenced before assignment