return empty set of races instead of null from SwissTimingraceTrackerImpl if no race was loaded

java/com.sap.sailing.domain.swisstimingadapter/src/com/sap/sailing/domain/swisstimingadapter/impl/SwissTimingRaceTrackerImpl.java

@@ -96,7 +96,8 @@ public class SwissTimingRaceTrackerImpl extends AbstractRaceTrackerImpl implemen
 
     @Override
     public Set<RaceDefinition> getRaces() {
-        return race==null?null:Collections.singleton(race);
+        final Set<RaceDefinition> emptySet = Collections.emptySet();
+        return race==null?emptySet:Collections.singleton(race);
     }
 
     @Override

java/com.sap.sailing.domain.test/src/com/sap/sailing/domain/test/WindEstimationOnConstructedTracksTest.java

@@ -132,7 +132,9 @@ public class WindEstimationOnConstructedTracksTest extends StoredTrackBasedTest
         assertTrue(combinedDegreesNow > 170 && combinedDegreesNow < 180);
         // we expect the combined direction now to be closer to the estimation as compared to before because the estimation is more confident
         // since the minimum cluster size is 2 instead of 1
-        assertTrue(combinedDegreesNow < combinedDegreesMinClusterSizeOne);
+        assertTrue("expected combinedDegreesNow ("+combinedDegreesNow+
+                ") < combinedDegreesMinClusterSizeOne ("+combinedDegreesMinClusterSizeOne+")",
+                combinedDegreesNow < combinedDegreesMinClusterSizeOne);
     }
 
     @Test