This is not the first time when I changed the oil on my 2011 Sentra and I noticed that there wasn't any used oil inside the old filter (Fram) . Anybody else noticed the same problem ???

Couple possibilities:

Did you take a dry paper towel to the interior of the filter? If the oil was relatively clean, and it drained overnight before your oil change, then all you'll see is some translucent areas on the paper.

The ADBV (anti drain back valve) CAN fail, but it's not likely unless the engine has been neglected badly.

I suspect if you were to cut the old filter open, the "dirty side" would have oil in it. I'm not a fan of Fram, nor are most real car enthusiasts, so let's try a different brand for your next oil change.

Keep us posted - I'm eager to see what you find out!

I suspect that the oil never made it inside the filter because of that rubber flap inside the top of the filter .