App crashed yet another time

[ChristianSch]

2015-10-24T16:48:52.035479+00:00 app[web.1]: /app/models/user.js:103
2015-10-24T16:48:52.035485+00:00 app[web.1]:                              ^
2015-10-24T16:48:52.035483+00:00 app[web.1]:         if (this.constructor.validateToken(token)) {
2015-10-24T16:48:52.035486+00:00 app[web.1]: TypeError: undefined is not a function
2015-10-24T16:48:52.035487+00:00 app[web.1]:     at model.UserSchema.methods.invalidateToken (/app/models/user.js:103:30)
2015-10-24T16:48:52.035488+00:00 app[web.1]:     at Query.<anonymous> (/app/api/v1/users/index.js:101:21)
2015-10-24T16:48:52.035487+00:00 app[web.1]:     at /app/api/v1/users/index.js:435:31
2015-10-24T16:48:52.035491+00:00 app[web.1]:     at process._tickDomainCallback (node.js:381:11)
2015-10-24T16:48:52.035489+00:00 app[web.1]:     at /app/node_modules/mongoose/node_modules/kareem/index.js:177:19
2015-10-24T16:48:52.035490+00:00 app[web.1]:     at /app/node_modules/mongoose/node_modules/kareem/index.js:109:16