Hi Middelburg,
Check this.. this.nationality.setSelectedKey('/Nationality'),
You are giving path but you are not binding the path value. I am thinking the above line you have check the syntax..
Do one thing get the values in an array and give that array values as below if there are 'n' number of values..
this.nationality.setSelectedKey(Nationality[0]), or if it is a single value give only 'Nationality'