make pass. none can only be passed in as a string

Author: leej3

heudiconv/dicoms.py

@@ -34,6 +34,7 @@ def group_dicoms_into_seqinfos(files, file_filter, dcmfilter, grouping):
     filegrp : dict
       `filegrp` is a dictionary with files groupped per each sequence
     """
+    if grouping == 'None': grouping = None
     allowed_groupings = ['studyUID', 'accession_number', None]
     if grouping not in allowed_groupings:
         raise ValueError('I do not know how to group by {0}'.format(grouping))