Hi Srikanth, __WithField seems to have trouble if the value type is generics. Rémi public final __ByValue class GenBug<E> { private final boolean value; private GenBug() { value = false; throw new AssertionError(); } public static <E> GenBug<E> create() { GenBug<E> bug = __MakeDefault GenBug<E>(); bug = __WithField(bug.value, true); return bug; } }