You can define a post-notification function that validates the comments fields and throws the error if its empty. The post-notification function is a PL/SQL procedure having the same API standards as that of function activities.
You can refer to workflow Developer guide for more details about defining the post notification function.
Simple example for 'TRANSFER' or 'FORWARD' operation is given below.
procedure Post_Notification (itemtype in varchar2,
itemkey in varchar2,
actid in varchar2,
funcmode in varchar2,
resultout in out nocopy varchar2) is
if funcmode in ('TRANSFER','FORWARD') then
select count(1) into l_count
where WF_ENGINE.context_new_role in ('SPIERSON','CBAKER');
--and/or any other conditions
if l_count<1 then
When a recipient responds, the Workflow Engine initially runs the post-notification function in VALIDATE mode which allows you to validate the response values before accepting the response. So you need to add your comments value validation for 'VALIDATE' mode (like funcmode in ('VALIDATE') )