made safe for empty wind tracks

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

@@ -1,6 +1,7 @@
 package com.sap.sailing.domain.test;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
@@ -19,6 +20,12 @@ import com.sap.sailing.domain.tracking.impl.WindTrackImpl;
 
 public class WindTest {
     private static final int AVERAGING_INTERVAL_MILLIS = 30000 /* 30s averaging interval */;
+    
+    @Test
+    public void testEmptyTrackYieldsNullAsWindEstimate() {
+        WindTrack track = new WindTrackImpl(AVERAGING_INTERVAL_MILLIS);
+        assertNull(track.getEstimatedWind(new DegreePosition(0, 0), MillisecondsTimePoint.now()));
+    }
 
     /**
      * If the wind track has areas with no data, and wind information is requested for such an interval,

java/com.sap.sailing.domain/src/com/sap/sailing/domain/tracking/impl/WindTrackImpl.java

@@ -138,7 +138,7 @@ public class WindTrackImpl extends TrackImpl<Wind> implements WindTrack {
                 } else {
                     beforeWind = null;
                 }
-            } else {
+            } else if (afterWind != null) {
                 if (afterIntervalStart == null) {
                     afterIntervalStart = afterWind.getTimePoint();
                 }
@@ -154,8 +154,12 @@ public class WindTrackImpl extends TrackImpl<Wind> implements WindTrack {
                 }
             }
         } while (beforeIntervalLength + afterIntervalLength < millisecondsOverWhichToAverage && (beforeWind != null || afterWind != null));
-        SpeedWithBearing avgWindSpeed = new KnotSpeedWithBearingImpl(knotSum / count, new DegreeBearingImpl(bearingDegSum/count));
-        return new WindImpl(p, at, avgWindSpeed);
+        if (count == 0) {
+            return null;
+        } else {
+            SpeedWithBearing avgWindSpeed = new KnotSpeedWithBearingImpl(knotSum / count, new DegreeBearingImpl(bearingDegSum/count));
+            return new WindImpl(p, at, avgWindSpeed);
+        }
     }
     
     @Override