code: public final void clearExtraTag(final String name) {
      if (extratags == null) {
        throw new IllegalStateException("no extra tags added");
      }
      if (extratags.get(name) == null) {
        throw new IllegalArgumentException("tag '" + name
            + "' not in" + extratags);
      }
      extratags.remove(name);
    }
docs: Clears a tag added using {@link #addExtraTag addExtraTag}.
  @param name The name of the tag to remove from the set of extra
  tags.
  @throws IllegalStateException if there's no extra tag currently
  recorded.
  @throws IllegalArgumentException if the given name isn't in the
  set of extra tags currently recorded.
  @see #addExtraTag