I was in the same situation as you, I called Canada Revenue Agency and told them about my 0 income year, they told me to declare it and I did. So, in your case, you have to declare 0 income for 2013-14 and get your Notice of Assessment. They'll usually mail it to you in 2 to 3 weeks. Then you may apply for citizenship.
From what I understood, even if you have 0 income, you still have to file your tax.