src/de/steamwar/sql/Referee.java

@@ -31,7 +31,7 @@ import java.util.stream.Collectors;
 public class Referee {
 
     private static final Table<Referee> table = new Table<>(Referee.class);
-    private static final SelectStatement<Referee> byEvent = table.select("eventID");
+    private static final SelectStatement<Referee> byEvent = table.selectFields("eventID");
 
     public static Set<Integer> get(int eventID) {
         return byEvent.listSelect(eventID).stream().map(referee -> referee.userID).collect(Collectors.toSet());