diff --git a/PRIVATE b/PRIVATE
index 144e72981..def4081e8 160000
--- a/PRIVATE
+++ b/PRIVATE
@@ -1 +1 @@
-Subproject commit 144e729811024fd5f99225fa10b6d8fa40e7d492
+Subproject commit def4081e837539dba7c4760abbb340553be66d3c
diff --git a/processing/post/addMises.py b/processing/post/addMises.py
index 35a6922c3..6593eeef8 100755
--- a/processing/post/addMises.py
+++ b/processing/post/addMises.py
@@ -38,9 +38,12 @@ parser.add_option('-s','--stress',
                   action = 'extend', metavar = '<string LIST>',
                   help = 'heading(s) of columns containing stress tensors')
 
+parser.set_defaults(strain = [],
+                    stress = [],
+                   )
 (options,filenames) = parser.parse_args()
 
-if options.stress is None and options.strain is None:
+if options.stress is [] and options.strain is []:
   parser.error('no data column specified...')
 
 # --- loop over input files -------------------------------------------------------------------------