docs: protected int getNumberOfSelectedMessages(HttpMessageContainer httpMessageContainer) {
          if (httpMessageContainer instanceof SelectableHttpMessagesContainer) {
              return ((SelectableHttpMessagesContainer) httpMessageContainer).getNumberOfSelectedMessages();
          } else if (httpMessageContainer instanceof SingleHttpMessageContainer) {
              return ((SingleHttpMessageContainer) httpMessageContainer).isEmpty() ? 0 : 1;
          }
  
          return 0;
      }