code: private ComboBox createModuleSelector() {
  
          ComboBox result = new ComboBox();
          result.setPageLength(20);
          result.setWidth("350px");
          result.setFilteringMode(FilteringMode.CONTAINS);
          result.setNewItemsAllowed(false);
          result.setNullSelectionAllowed(false);
          List<String> moduleNames = Lists.newArrayList();
          for (CmsModule module : OpenCms.getModuleManager().getAllInstalledModules()) {
              String moduleName = module.getName();
              if (!m_moduleCheckboxes.containsKey(moduleName)) {
                  moduleNames.add(moduleName);
              }
          }
          Collections.sort(moduleNames);
          for (String moduleName : moduleNames) {
              result.addItem(moduleName);
          }
  
          return result;
      }
docs: Creates a new module selector, containing only the modules for which no check box is already displayed.<p>
  
  @return the new module selector