### Question:
ExternalMechanism extends AbstractMechanism { @Override public byte[] getInitialResponse() { return EMPTY; }  @Override byte[] getInitialResponse(); @Override byte[] getChallengeResponse(byte[] challenge); @Override int getPriority(); @Override String getName(); @Override boolean isApplicable(String username, String password, Principal localPrincipal);  }### Answer:
@Test public void testGetInitialResponseWithNullUserAndPassword() { ExternalMechanism mech = new ExternalMechanism(); byte[] response = mech.getInitialResponse(); assertNotNull(response); assertTrue(response.length == 0); }