code: void report(Class c) {
          if (!get().contains(c)) {
              try {
                  append(c.getName());
              } catch (IOException e) {
                  LOGGER.log(Level.WARNING, "Failed to persist " + file, e);
              }
          }
      }
docs: This method gets called every time we see a new type of callable that we reject,
  so that we can persist the list.