### Question:
EmptyConstructor implements EmptyTreeConstructor<E, MutableSettableNode<E>, MutableTreeImpl<E>> { @Override public Class<? extends Tree> forClass() { return MutableTreeImpl.class; }  @Override final MutableTreeImpl<E> build(); @Override Class<? extends Tree> forClass();  }### Answer:
@Test public void key() { final EmptyConstructor<String> constructor = new EmptyConstructor<>(); assertEquals(MutableTreeImpl.class, constructor.forClass()); }