### Question:
ExtraField { static void register(final Class<? extends ExtraField> c) { final ExtraField ef; try { ef = c.getDeclaredConstructor().newInstance(); } catch (NullPointerException ex) { throw ex; } catch (Exception ex) { throw new IllegalArgumentException(ex); } final int headerId = ef.getHeaderId(); assert UShort.check(headerId); registry.put(headerId, c); }    }### Answer:
@Test public void testRegister() { try { ExtraField.register(null); fail(); } catch (NullPointerException expected) { } try { ExtraField.register(TooSmallHeaderIDExtraField.class); fail(); } catch (IllegalArgumentException expected) { } try { ExtraField.register(TooLargeHeaderIDExtraField.class); fail(); } catch (IllegalArgumentException expected) { } ExtraField.register(NullExtraField.class); }