dataset.get_files('latest') fails

[tomck]

Using an existing dataset with several files in it, I get an error.

Python 2.7.9 (default, Jun 27 2016, 20:10:46)
[GCC 4.4.7 20120313 (Red Hat 4.4.7-11)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from dataverse import Connection
>>> host = 'hostname.example.com'
>>> token = 'token-code-'
>>> connection = Connection(host, token)
>>> dataverse = connection.get_dataverse('test')
>>> dataset = dataverse.get_dataset_by_doi('DOI:10.5072/FK2/ZDNXKZ')
>>> files = dataset.get_files('latest')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'get_files'

Not sure why. Happened on DV 4.3.1 and 4.4.0.