### Question:
DiffTree extends AbstractGeoGigOp<Iterator<DiffEntry>> implements
        Supplier<Iterator<DiffEntry>> { public DiffTree setOldVersion(String oldRefSpec) { this.oldRefSpec = oldRefSpec; return this; } DiffTree(); DiffTree setOldVersion(String oldRefSpec); DiffTree setNewVersion(String newRefSpec); DiffTree setOldTree(ObjectId oldTreeId); DiffTree setNewTree(ObjectId newTreeId); DiffTree setPathFilter(@Nullable String path); DiffTree setPathFilter(@Nullable List<String> pathFitlers); DiffTree setBoundsFilter(@Nullable ReferencedEnvelope bounds); DiffTree setCustomFilter(@Nullable Predicate<Bounded> customFilter); DiffTree setChangeTypeFilter(@Nullable ChangeType changeType); @Override Iterator<DiffEntry> get(); DiffTree setReportTrees(boolean reportTrees); DiffTree setRecursive(boolean recursive);  }### Answer:
@Test public void testNoNewVersionSet() { exception.expect(NullPointerException.class); exception.expectMessage("new version"); diffTree.setOldVersion(Ref.HEAD).call(); }