code: String getFacetParamKey(String facet) {
  
          I_CmsSearchControllerFacetField fieldFacet = m_result.getController().getFieldFacets().getFieldFacetController().get(
              facet);
          if (fieldFacet != null) {
              return fieldFacet.getConfig().getParamKey();
          }
          I_CmsSearchControllerFacetRange rangeFacet = m_result.getController().getRangeFacets().getRangeFacetController().get(
              facet);
          if (rangeFacet != null) {
              return rangeFacet.getConfig().getParamKey();
          }
          I_CmsSearchControllerFacetQuery queryFacet = m_result.getController().getQueryFacet();
          if ((queryFacet != null) && queryFacet.getConfig().getName().equals(facet)) {
              return queryFacet.getConfig().getParamKey();
          }
  
          // Facet did not exist
          LOG.warn(Messages.get().getBundle().key(Messages.LOG_FACET_NOT_CONFIGURED_1, facet), new Throwable());
  
          return null;
      }
docs: Returns the parameter key of the facet with the given name.
  @param facet the facet's name.
  @return the parameter key for the facet.