CA PPM 15.4, 15.5, 15.5.1
The defect has been fixed in CA PPM 15.6.
The issues happens when the list has one or more resources without a Avatar for their accounts. Login to PPM as anyone of those resources and add an Avatar for that user. Try to replicate by problem and the line corresponding to that resource, who just added an avatar, will not be there anymore in the app-ca.log. This could be verified through the Resource ID that is displayed in the error message.