code: public void setCategories(List<String> categories) {
  
          if ((categories != null) && !categories.isEmpty()) {
              addFilterQuery(CmsSearchField.FIELD_CATEGORY + CmsSearchField.FIELD_DYNAMIC_EXACT, categories, true, true);
          }
      }
docs: Sets the categories only if not set in the query parameters.<p>
  
  @param categories the categories to set