### Question:
PlainMechanism extends AbstractMechanism { @Override public byte[] getInitialResponse() { String username = getUsername(); String password = getPassword(); if (username == null) { username = ""; } if (password == null) { password = ""; } byte[] usernameBytes = username.getBytes(StandardCharsets.UTF_8); byte[] passwordBytes = password.getBytes(StandardCharsets.UTF_8); byte[] data = new byte[usernameBytes.length + passwordBytes.length + 2]; System.arraycopy(usernameBytes, 0, data, 1, usernameBytes.length); System.arraycopy(passwordBytes, 0, data, 2 + usernameBytes.length, passwordBytes.length); return data; }  @Override int getPriority(); @Override String getName(); @Override byte[] getInitialResponse(); @Override byte[] getChallengeResponse(byte[] challenge); @Override boolean isApplicable(String username, String password, Principal localPrincipal);  }### Answer:
@Test public void testGetInitialResponseWithNullUserAndPassword() { PlainMechanism mech = new PlainMechanism(); byte[] response = mech.getInitialResponse(); assertNotNull(response); assertTrue(response.length > 0); }