@Override
  public void putAll(Map<? extends CharSequence, ? extends V> otherMap) {
    otherMap.forEach(this::put);
  }
@Test
  public void testPutAll() {
    CharSequenceMap<String> map = CharSequenceMap.create();
    map.putAll(ImmutableMap.of("key1", "value1", "key2", "value2"));
    assertThat(map).containsEntry("key1", "value1");
    assertThat(map).containsEntry("key2", "value2");
  }