### Question:
MnemonicCode { public static byte[] toSeed(List<String> words, String passphrase) { checkNotNull(passphrase, "A null passphrase is not allowed."); String pass = Utils.SPACE_JOINER.join(words); String salt = "mnemonic" + passphrase; final Stopwatch watch = Stopwatch.createStarted(); byte[] seed = PBKDF2SHA512.derive(pass, salt, PBKDF2_ROUNDS, 64); watch.stop(); log.info("PBKDF2 took {}", watch); return seed; } MnemonicCode();  MnemonicCode(InputStream wordstream, String wordListDigest); List<String> getWordList(); static byte[] toSeed(List<String> words, String passphrase); byte[] toEntropy(List<String> words); List<String> toMnemonic(byte[] entropy); void check(List<String> words); static long BIP39_STANDARDISATION_TIME_SECS; static MnemonicCode INSTANCE; }### Answer:
@Test(expected = NullPointerException.class) public void testNullPassphrase() throws Exception { List<String> code = split("legal winner thank year wave sausage worth useful legal winner thank yellow"); MnemonicCode.toSeed(code, null); }
@Test(expected = NullPointerException.class) public void testNullPassphrase() throws Exception { List<String> code = WHITESPACE_SPLITTER.splitToList("legal winner thank year wave sausage worth useful legal winner thank yellow"); MnemonicCode.toSeed(code, null); }