The SiblingColumnStorageStrategy uses a visitor to find the value of the sibling column in order to generate the unique resource name. When the visitor is running over the AttributeGroup, this class is logging some debug information and try to use the resource name. This is the goal of the visitor, so that is generating an infinite-loop.

An easy fix is to change the toString method of the AttributeGroup to avoid call the toString method of SnmpCollectionResource, and that way avoid the loop.