### Question:
SimpleKeyCryptoBuilder extends KeyCryptoBuilder { @Override public KeyCryptoBuilder setKeySalt(final String keySalt) { if (keySalt == null) { throw new NullPointerException("Key salt cannot be null."); } this.keySalt = keySalt; markAsSet(Attribute.KEY_SALT); return this; }  @Override KeyCryptoProduct build(); @Override KeyCryptoBuilder setKeySalt(final String keySalt); @Override KeyCryptoBuilder setPrivateKey(final URI privateKey); @Override KeyCryptoBuilder setServerAddress(final URI serverAddress); @Override KeyCryptoBuilder setUsername(final String username);  }### Answer:
@Test(expected = NullPointerException.class) public void testNullKeySalt() { builder.setKeySalt(null); }