return transformValues(table, FIRST_CHARACTER);
  }

  // Null support depends on the underlying table and function.
  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  @Override
  public void testNullPointerInstance() {}

  // put() and putAll() aren't supported.
  @Override
  public void testPut() {
    assertThrows(UnsupportedOperationException.class, () -> table.put("foo", 1, 'a'));
    assertSize(0);
  }