According to the Montreux convention, Turkey should block the Bosphore to any military ship, unless they are returning to their home base.
In time of war, Turkey not being belligerent, warships of belligerent Powers shall not pass, except i.a. to return to their base. (art. 19)
I'm not sure how this military ship can enter thr Black sea.
Niger is a 25M inhabitants country. A couple of demonstrations supported by Russian don't reflect the global reality.