docs: public static <P, T> PositionFactory<P, T> optional(Function<? super P, ? extends T> accessor) {
          Validate.isInstanceOf(Accessor.class, accessor, "Cannot detect property from %s; missing %s?", accessor,
              THERIAN_PROPERTY_METHOD_WEAVER);
          final boolean optional = true;
          return new PositionFactory<>(((Accessor<? super P, ? extends T>) accessor).propertyName, optional);
      }