### Question:
TrieId implements Serializable { public int addWord(String word) { if (word == null || word.length() == 0) throw new IllegalArgumentException("word cannot be null or empty"); Integer id = trie.getWordData(word); if (id == null) { id = maxId; trie.addWord(word, id); maxId++; return id; } else { return id; } } TrieId();  TrieId(boolean caseSensitive); int getSize(); int addWord(String word); int getWordId(String word); void toIdsFile(OutputStream os); @SuppressWarnings("resource") static TrieId fromIdsFile(InputStream is);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void testEmptyString() { TrieId t = new TrieId(); t.addWord(""); }