docs: protected static void checkChannels(final Iterable<String> channels) {
          if (channels == null) {
              throw new IllegalArgumentException("channels must not be null");
          }
          for (final String channel : channels) {
              if (channel == null || "".equals(channel)) {
                  throw new IllegalArgumentException("channels' members must not be null: " + channels);
              }
          }
      }