bug fix.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@3794 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/maven/MavenModuleSetBuild.java

@@ -120,7 +120,7 @@ public final class MavenModuleSetBuild extends AbstractBuild<MavenModuleSet,Mave
 
         for (MavenModule m : mods) {
             MavenBuild b = m.getNearestOldBuild(end - 1);
-            if(b.getNumber()>=getNumber())
+            if(b!=null && b.getNumber()>=getNumber())
                 r.put(m,b);
         }