reverts signature default val for userid in delete_instances() for no…

…w, re #10781

arches/app/models/graph.py

@@ -564,7 +564,7 @@ def delete(self):
                 )
             )
 
-    def delete_instances(self, userid=None, verbose=False):
+    def delete_instances(self, userid={}, verbose=False):
         """
         deletes all associated resource instances