### Question:
EmptyConstructor implements EmptyTreeConstructor<E, MutableSettableNode<E>, MutableTreeImpl<E>> { @Override public final MutableTreeImpl<E> build() { return new MutableTreeImpl<>(null, new FixedUncheckedSimpleCollection<>(new Object[0])); }  @Override final MutableTreeImpl<E> build(); @Override Class<? extends Tree> forClass();  }### Answer:
@Test public void build() { final EmptyConstructor<String> constructor = new EmptyConstructor<>(); final MutableTreeImpl<String> tree = constructor.build(); assertTrue(tree.isEmpty()); }