After allowing Anonymous users to post on SharePoint 2013 everything works fine except for the WebPart that is meant to show users' comments. this is the error it displays after adding an Anonymous comment:

TypeError: Unable to get value of the property 'trim': object is null or undefined

TypeError: Unable to get value of the property 'trim': object is null or undefined

Once you clear the Anonymous comment everything goes back to normal.

My farm is on Feb 2015 CU. Is this by design or is it a bug?

Hi,

As I understand, it display errors after adding anonymous comment in SharePoint 2013.

You could create the custom web part programmatically for anonymous comments. For more detailed information, you could refer to the articles below.

The article below is about how to create a Custom Web part in SharePoint 2013.

http://www.learningsharepoint.com/2012/12/24/how-to-create-a-custom-webpart-in-sharepoint-2013/

The article below is about how to create a new Visual Web Part for SharePoint 2013 with Visual Studio 2012.

http://www.ashokraja.me/articles/How-to-create-a-new-Visual-WebPart-in-SharePoint-2013-with-Visual-Studio-2012

There is a similar case:

https://social.technet.microsoft.com/Forums/office/en-US/254214ed-b0ea-4175-9041-62fe2ae957a1/posting-anonymous-comments-on-an-internal-sharepoint-2013-blog?forum=sharepointgeneral

Best regards,

Sara Fan