vnconfig(8) is a tool to create virtual disk images. There was a (not officially filed) bug report that it sometimes returns success although it fails:

qemu# vnconfig vnd0 not_existent_file ; echo $? ;: bad
vnconfig: not_existent_file: No such file or directory
0
qemu# vnconfig vnd0 existent_file ; echo $? ;: good
0
qemu# 

In this task, you will go through the whole work of fixing a bug: You have to analyze the situation, find the source of that bug in the code, and finally fix it.