Do you need to pay any taxes if you have zero income in a year?

I will be taking a year off of work and not planning on making any income at all and living off of selling some RSU's from work. From what I am reading, if the RSU's are considered to be held long term, and my W2 income goes to zero, I would owe 0% in capital gains as long term stock sales do not count as income.

Am I missing something?