Check for undefined explicitly. Fixes #953.
Check for undefined explicitly. Fixes #953.

Value 0 didn't work as expected with the previous check.

CorvusCorrax/knex,statyan/knex,vellotis/knex,tgriesser/knex,juanjoLenero/knex,harriha/knex,sanchesic89/knex,statyan/knex,chrisbroome/knex,whitelynx/knex,WaltRock/knex,vellotis/knex,knax/knex-bower,chuym/knex,joeframbach/knex,noodle/knex,harriha/knex,abegines/knex,joeframbach/knex,nkt/knex,noodle/knex,blah238/knex,tgriesser/knex,galenandrew/knex,joeframbach/knex,whitelynx/knex,maxcnunes/knex,realtymaps/knex,chuym/knex,chrisbroome/knex,wubzz/knex,realtymaps/knex,sanchesic89/knex,Atlantis-Software/knex,techniq/knex,chrisbroome/knex,shutterstock/knex,galenandrew/knex,knax/knex-bower,galenandrew/knex,carragom/knex,blah238/knex,tgriesser/knex,WaltRock/knex,knax/knex-bower,techniq/knex,realtymaps/knex,sxhao/knex,blah238/knex,maxcnunes/knex,juanjoLenero/knex,vellotis/knex,harriha/knex,abegines/knex,juanjoLenero/knex,shutterstock/knex,carragom/knex,shutterstock/knex,nkt/knex,wubzz/knex,sanchesic89/knex,techniq/knex,maxcnunes/knex,nkt/knex,sxhao/knex,whitelynx/knex,Atlantis-Software/knex,chuym/knex,sxhao/knex,CorvusCorrax/knex