CleverRaven/Cataclysm-DDA — pull request #7765 by kevingranade (2014-05-28 06:54:23+00:00)
Title: Check for null string in addition to no string.

Reported here: http://smf.cataclysmdda.com/index.php?topic=6541.0
To reproduce error, spawn a car, open a door, spawn a hacksaw and wrench, give yourself some skills, uninstall the door.
It prints an error and generates a "steel frame with undefined-s", which is a container of steel frame... liquid.