Creating a bag from a remote file manifest raises an exception

[NickolausDS]

When creating a bag with the following command:

$ bdbag bag/ --remote-file-manifest manifest.json

An error is raised:

RuntimeError: Expected the same number of files for each checksum

Details about the above command:

• Run with Bagit version bagit==1.6.2
• Run with BDBag version bdbag==1.1.1
• bag/ in the command above is an empty directory
• manifest.json corresponds to the example in the docs

This didn't seem to happen on previous versions. Before, it allowed me to create an 'empty' bdbag with a fetch file that could be used to pull down the remote files and validate them.

[mikedarcy]

Unfortunately, this is an issue with bagit-1.6.x and some new error checking logic which basically is prohibiting the bagging of an empty directory. I can reproduce this with just bagit ./bag/ on an empty directory. This worked in bagit-1.5.4 and I think needs to continue to work. There is a pretty easy one line fix for this in bagit.py so I will file a PR with bagit and see what they have to say.

[mikedarcy]

Filed a PR for bagit: LibraryOfCongress/bagit-python#100