Don't crash when app spec doesn't supply categories.
Don't crash when app spec doesn't supply categories.

johnwallace123/dx-toolkit,johnwallace123/dx-toolkit,jhuttner/dx-toolkit,andyshinn/dx-toolkit,andyshinn/dx-toolkit,jhuttner/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,andyshinn/dx-toolkit,johnwallace123/dx-toolkit,andyshinn/dx-toolkit,olegnev/dx-toolkit,johnwallace123/dx-toolkit,johnwallace123/dx-toolkit,olegnev/dx-toolkit,jhuttner/dx-toolkit,olegnev/dx-toolkit,olegnev/dx-toolkit,jhuttner/dx-toolkit,olegnev/dx-toolkit,olegnev/dx-toolkit,jhuttner/dx-toolkit,andyshinn/dx-toolkit,dnanexus/dx-toolkit,olegnev/dx-toolkit,dnanexus/dx-toolkit,dnanexus/dx-toolkit,jhuttner/dx-toolkit,andyshinn/dx-toolkit,jhuttner/dx-toolkit,andyshinn/dx-toolkit,andyshinn/dx-toolkit,dnanexus/dx-toolkit,johnwallace123/dx-toolkit,olegnev/dx-toolkit,jhuttner/dx-toolkit