fix: added null checks to remove home/away games

src/main/java/cz/muni/fi/pa165/icehockeymanager/services/TeamServiceImpl.java

@@ -71,12 +71,18 @@ public class TeamServiceImpl implements TeamService {
 
     @Override
     public void removeHomeGame(Team homeTeam, Game game) {
+        if (game == null) {
+            throw new NullPointerException("The game is null");
+        }
         homeTeam.removeHomeGame(game);
         teamDao.update(homeTeam);
     }
 
     @Override
     public void removeAwayGame(Team awayTeam, Game game) {
+        if (game == null) {
+            throw new NullPointerException("The game is null");
+        }
         awayTeam.removeAwayGame(game);
         teamDao.update(awayTeam);
     }