In current lworld, this code:

Object d2 = y.Z.default;

Will give a strange error:

test/langtools/tools/javac/valhalla/lworld-values/UnknownTypeDefault.java:12: error: package y does not exist
Object d2 = y.Z.default;
^

This should work more like the error for
Object d1 = Y.default;

which is
test/langtools/tools/javac/valhalla/lworld-values/UnknownTypeDefault.java:11: error: cannot find symbol
Object d1 = Y.default;
^
  symbol: class Y
  location: class UnknownTypeDefault