code: public int getCodec(final Class<?> clazz) {
      if (clazz == null) {
        throw new IllegalArgumentException("Clazz cannot be null.");
      }
      final Integer id = codecs_ids.get(clazz);
      if (id == null) {
        throw new IllegalArgumentException("No codec ID assigned to class " 
            + clazz);
      }
      return id;
    }
docs: Return the ID of the given codec.
  @param clazz The non-null class to search for.
  @return The ID of the codec.
  @throws IllegalArgumentException if the class was null or no ID was assigned
  to the class.