@Test
public void mutable() {

    ListValue lv = PropertyValue.createList("foo");
    lv.addList();
    assertThat(lv.isImmutable()).isFalse();
    ListValue lv2 = lv.mutable();
    assertThat(lv2.isImmutable()).isFalse();
    assertThat(lv == lv2).isTrue();
}