code: private ComboBox prepareComboBox(IndexedContainer container, String captionKey) {
  
          ComboBox result = new ComboBox(CmsVaadinUtils.getWpMessagesForCurrentLocale().key(captionKey), container);
          result.setTextInputAllowed(true);
          result.setNullSelectionAllowed(false);
          result.setWidth("100%");
          result.setInputPrompt(
              Messages.get().getBundle(UI.getCurrent().getLocale()).key(Messages.GUI_EXPLORER_CLICK_TO_EDIT_0));
          result.setItemCaptionPropertyId(CAPTION_PROPERTY);
          result.setFilteringMode(FilteringMode.CONTAINS);
          return result;
      }
docs: Prepares a combo box.<p>
  
  @param container the indexed item container
  @param captionKey the caption message key
  
  @return the combo box