I'm a Finnish citizen and have spent the last 6 years in the US. I finished a Ph.D. in May last year and I was on a J-1 visa until February last year. At that point I switched over to a G-4 visa due to my wife's work. Since graduation I've worked in the US as a G-4 dependent on an EAD, so I owe US taxes for that.
Now my problem is that the IRS has the so called "substantial presence test". Last year and in the years before that, I always satisfied the substantial presence test, so I was considered a resident for tax purposes. The problem with the G-4 visa is that days spent in the US in that status are not counted for the test.
I traveled quite a bit in 2014/2013 visiting a few research institutes abroad for extended periods of time, so that when I do the substantial presence test for last year, I don't go over the limit, i.e. the test doesn't consider me a tax resident. The problem is that I'm not resident anywhere now it seems. Finland doesn't even require me to file taxes anymore, because I've been abroad long enough.
Is there a requirement to be a tax resident somewhere? Should it be the US in my case? How do I communicate such a thing to the IRS in my tax return if that is the case?