In SystemDictionary::resolve_from_stream() we have this:

  // Make sure that we didn't leave a place holder in the
  // SystemDictionary
  debug_only( {
    MutexLocker mu(SystemDictionary_lock);

    oop check = find_class_or_placeholder(class_name, class_loader);
    assert(check->is_klass(), "found symbol oop, should have been a klass");

    oop check2 = find_class_or_placeholder(k->name(), k->class_loader());
    assert(check == check2, "name inconsistancy in SystemDictionary");
  } );

The first assert is too strong, it is legal for class_name to
be null. The SystemDictionary fires another assert when we attempt to
probe for the null class_name.