The user is notified of a poll error only after they submit the poll and the page is redirected. Invalid polls can be verified before poll submission like Web Form Portlet, Form, and DDL.
When the poll has no selection the user is notified of the error before submitting the poll and being redirected.
Steps to Reproduce:
1) Add a Polls Portlet to the page
2) Create a valid Poll and display it in the Polls Portlet
3) Submit the poll without selecting any option