[This](https://github.com/itpatrol/alttracker/blob/master/alttracker.pages.inc#L88) will throw critical exception when user will have no at least one node. You need to add checking that array of nids is not empty before function [alttracker_nodes_load](https://github.com/itpatrol/alttracker/blob/master/alttracker.pages.inc#L123) will be invoked in row 88.
This will throw critical exception when user will have no at least one node.
You need to add checking that array of nids is not empty before function alttracker_nodes_load will be invoked in row 88.