Better fix for expr_eval of action['email'] for issue838

tryton/gui/window/view_form/view/list.py

@@ -265,8 +265,8 @@ class ViewList(ParserView):
             message(_('No record selected!'), self.window)
             return False
         email = {}
-        if 'email' in action:
-            email = self.screen.current_model.expr_eval(action['email'] or '')
+        if action.get('email'):
+            email = self.screen.current_model.expr_eval(action['email'])
             if not email:
                 email = {}
         email['subject'] = action['name'].replace('_', '')