Minor validation fixes and toString changes in Leg, fixed LegTest exception expectation

dddsample/src/main/java/se/citerus/dddsample/domain/model/cargo/Leg.java

     Validate.notNull(voyage, "Voyage is required");
     Validate.notNull(loadLocation, "Load location is required");
     Validate.notNull(unloadLocation, "Unload location is required");
+    Validate.notNull(loadTime, "Load time is required");
+    Validate.notNull(unloadTime, "Unload time is required");
     Validate.isTrue(!loadLocation.sameIdentityAs(unloadLocation));
     // TODO use a minimum time between unloading and loading?
     Validate.isTrue(unloadTime.after(loadTime));
   @Override
   public String toString() {
     return "Load in " + loadLocation + " at " + loadTime +
-      ", unload in " + unloadLocation + " at " + unloadTime;
+      " --- Unload in " + unloadLocation + " at " + unloadTime;
   }
 
   Leg() {

dddsample/src/test/java/se/citerus/dddsample/domain/model/cargo/LegTest.java

 
   final Voyage voyage = NEW_YORK_TO_DALLAS;
 
-  @Test(expected = IllegalArgumentException.class)
+  @Test(expected = NullPointerException.class)
   public void testConstructor() throws Exception {
     Leg.deriveLeg(null, null, null);
   }