@Test
  public void genericOptionalOfNullable() {
    ConcreteOptional empty = ConcreteOptional.builder().build();
    assertThat(empty.optional()).isEmpty();
    ConcreteOptional notEmpty = ConcreteOptional.builder().setOptional("foo").build();
    assertThat(notEmpty.optional()).hasValue("foo");
  }
Like {@link AutoValueTest}, but with code that doesn't build with at least some versions of
Eclipse, and should therefore not be included in {@link CompileWithEclipseTest}. (The latter is
not currently present in the open-source build.)
value/src/it/functional/src/test/java/com/google/auto/value/AutoValueNotEclipseTest.java