Incorrect behavior when using Prefix

[mikemiles-dev]

On S3 when using paginatior to list files if you pass the prefix key but a blank value you get back the contents key in the response however on fake s3 if you do the same you get a common prefix key in the response and no contents.

[abrugh]

To elaborate this is with boto3's list_objects, paginator.paginate function. If a delimiter and prefix of '' are passed to the paginate function real s3 works but fake-s3 does not. The work around seems to be to not pass those args to paginate.