code: protected List<HttpMessage> getSelectedMessages(HttpMessageContainer httpMessageContainer) {
          if (httpMessageContainer instanceof SelectableHttpMessagesContainer) {
              return ((SelectableHttpMessagesContainer) httpMessageContainer).getSelectedMessages();
          } else if (httpMessageContainer instanceof SingleHttpMessageContainer) {
              SingleHttpMessageContainer singleMessageContainer = (SingleHttpMessageContainer) httpMessageContainer;
              if (!singleMessageContainer.isEmpty()) {
                  List<HttpMessage> selectedHttpMessages = new ArrayList<>(1);
                  selectedHttpMessages.add((((SingleHttpMessageContainer) httpMessageContainer).getMessage()));
                  return selectedHttpMessages;
              }
          }
  
          return Collections.emptyList();
      }
docs: Returns the selected messages of the given message container.
  <p>
  By default it returns the selected messages from {@code SelectableHttpMessagesContainer}s and for
  {@code SingleHttpMessageContainer}s returns the contained message or empty {@code List} if none.
  </p>
  <p>
  Normally overridden if other implementations of {@code HttpMessageContainer} are supported. Default are
  {@code SingleHttpMessageContainer} and {@code SelectableHttpMessagesContainer}.
  </p>
  
  @param httpMessageContainer the container that will be evaluated
  @return a {@code List} containing the selected messages
  @see #isButtonEnabledForSelectedMessages(List)
  @see #isSelectedMessagesInSessionScope(HttpMessageContainer)
  @see SingleHttpMessageContainer
  @see SelectableHttpMessagesContainer