don't log and raise for the same exception

Author: Shoshana Berleant

nipype/workflows/dmri/connectivity/group_connectivity.py

@@ -461,8 +461,7 @@ def create_average_networks_by_group_workflow(group_list, data_dir, subjects_dir
         l4infosource.inputs.group_id1 = list(group_list.keys())[0]
         l4infosource.inputs.group_id2 = list(group_list.keys())[1]
     except IndexError as e:
-        print('The create_average_networks_by_group_workflow requires 2 groups')
-        raise_from(Exception(), e)
+        raise_from(Exception('The create_average_networks_by_group_workflow requires 2 groups'), e)
 
     l4info = dict(networks=[['group_id', '']], CMatrices=[['group_id', '']], fibmean=[['group_id', 'mean_fiber_length']],
                   fibdev=[['group_id', 'fiber_length_std']])