State.py: robustness improvement; in some rare cases, DC workflow may have...

State.py: robustness improvement; in some rare cases, DC workflow may have non-exist but defined as possible transitions. this improvement can avoid these error crush workflow conversion.

product/ERP5Workflow/Document/State.py

@@ -67,10 +67,11 @@ class State(IdAsReferenceMixin("state_", "prefix"), XMLObject, XMLMatrix):
 
   def addPossibleTransition(self, tr_ref):
     possible_transition_list = self.getCategoryList()
-    transition = self.getParent()._getOb('transition_'+tr_ref)
-    tr_path = 'destination/' + '/'.join(transition.getPath().split('/')[2:])
-    possible_transition_list.append(tr_path)
-    self.setCategoryList(possible_transition_list)
+    transition = self.getParent()._getOb('transition_'+tr_ref, None)
+    if transition is not None:
+      tr_path = 'destination/' + '/'.join(transition.getPath().split('/')[2:])
+      possible_transition_list.append(tr_path)
+      self.setCategoryList(possible_transition_list)
 
   def setPermission(self, permission, acquired, roles, REQUEST=None):
       """Set a permission for this State."""