docs: public ThumborUrlBuilder filter(String... filters) {
      if (filters.length == 0) {
        throw new IllegalArgumentException("You must provide at least one filter.");
      }
      if (this.filters == null) {
        this.filters = new ArrayList<String>(filters.length);
      }
      for (String filter : filters) {
        if (filter == null || filter.length() == 0) {
          throw new IllegalArgumentException("Filter must not be blank.");
        }
        this.filters.add(filter);
      }
      return this;
    }