title: FFT of a 2d array with NAN
body: <p>I'm trying to apply FFT on a 2D array with NAN. I don't want to replace the NAN values with anything. Is there a way to apply FFT and ignore the NAN values?</p>
  
  <pre><code>arr=np.array([[1, 2, 3], [4, NAN, 6], [1, 2, NAN]])
  f=np.fft.fft2(arr)
  </code></pre>