Would I need a letter from my US employer and a joint sponsor for the I-864 sponsorship of a foreign spouse if I didn't have any income for the past 3 years (2015, 2014, 2013 income 0) but have been employed only since February 2016? What is the minimum duration that I need to be employed (is it 6 month?) in order to file the I-864 without the need of obtaining a letter from my employer and/or adding a joint sponsor, and not have US Immigration Services reject my Petition for Alien Relative?