in python-swiftclient/swiftclient/service.py,
there is a method
def download(self, container=None, objects=None, options=None):
if container is specified but objects not, it download all
objects in specified container.
if both container and objects are specified, it download all
specified objects in the container.
when it comes to the case that, objects argument is specified,
but it turned out to be empty array [ ], the download method
download all the objects under specified container.
this may be not reasonable.
for example,
the objects was not empty when it came from command line,
but it's filtered, maybe by --prefix argument.
at last, it turned out to be empty array.
when calling download method with objects arguments
being empty array, we should download nothing instead of
all the objects under the specified container.
Change-Id: I81aab935533a50b40679c8b3575f298c285233a8
Closes-bug: #1549881