Steps to reproduce: 1. Add RadTreeView with few items 2. Apply custom filtering 3. In order to remove the custom filtering and return the default filtering, set the FilterPredicate to null. As a result, it is thrown an exception. Workaround: 1. Save the default filter predicate before applying the custom filtering 2. Clear filter descriptors and set the FilterPredicate property to stored default filter predicate In the attachments can be found a sample application demonstrating the issue and the workaround