The "Previous" option in the first topic of an exercise and "Next" option in the last topic of an exercise results in "Notice"

The "Previous" option in the first topic of an exercise and "Next" option in the last topic of an exercise results in "Notice" stating that the requested document could not be found.
The "Previous" option in first topic of an exercise and "Next" option in last topic of an exercise needs to be removed.

Steps:
1. Go to : http://next.dev.curriki.org/xwiki/bin/view/Coll_Group_CurrikiGeometry/KhanQuizzes?skin=respurriki
2. Select an exercise
3. Go to first topic in exercise and click Previous.
4. Go to last topic in exercise and click Next.