fix IsGlobalAggregation

@@ -34,9 +34,9 @@ public class IsGlobalAggregation extends AbstractAggregation {
 			Bucket bucket = itAgg.next();
 			String bool = bucket.getKeyAsString();
 			if ("Y".equals(bool)) {
-				return true;
+				return Boolean.TRUE;
 			}
 		}
-		return false;
+		return Boolean.FALSE;
 	}
 }