Please list the nick names of the coaches who are from the USA and have taught the Buffalo Sabres.
from the USA refers to birthCountry = 'USA'; nick names of the coaches refer to nameNick where coachID is not NULL ; Buffalo Sabres is the name of team;
SELECT DISTINCT nameNick FROM Coaches AS T1 INNER JOIN Teams AS T2 ON T1.year = T2.year AND T1.tmID = T2.tmID INNER JOIN Master AS T3 ON T1.coachID = T3.coachID WHERE T2.name = 'Buffalo Sabres' AND T3.birthCountry = 'USA'