We previously had a fatal error make it to deploy train because one of the variables sent to processTemplate was undefined: T161735

We need to patch https://gerrit.wikimedia.org/r/#/c/339941/ to make sure that doesn't happen with that one before it gets deployed (Thurs). Mustache can handle undefined variables but it appears that processTemplate cannot.

It would probably be good just to define all the variables at the top of the file that are getting to processTemplate to ensure they're all defined.