public void test_withCorrectedTo_nullToNull() {
   VersionCorrection test = VersionCorrection.of(INSTANT1, null);
   assertEquals(VersionCorrection.of(INSTANT1, null), test.withCorrectedTo(null));
 }
 public void test_withCorrectedTo_nullToInstant() {
   VersionCorrection test = VersionCorrection.of(INSTANT1, null);
   assertEquals(VersionCorrection.of(INSTANT1, INSTANT3), test.withCorrectedTo(INSTANT3));
 }