What is the nationality of the 7th season Purple Cap winner?
nationality refers to Country_Name; the 7th season refers to Season_Id = 7; Purple Cap winner refers to Purple_Cap IS NOT NULL
SELECT T3.Country_Name FROM Season AS T1 INNER JOIN Player AS T2 ON T1.Man_of_the_Series = T2.Player_Id INNER JOIN Country AS T3 ON T2.Country_Name = T3.Country_Id WHERE T1.Season_Id = 7 AND T1.Purple_Cap IS NOT NULL