code: public CmsSolrIndex getIndexSolr(String indexName) {
  
          I_CmsSearchIndex index = getIndex(indexName);
          if (index instanceof CmsSolrIndex) {
              return (CmsSolrIndex)index;
          }
          return null;
      }
docs: Returns the Solr index configured with the given name.<p>
  The index must exist, otherwise <code>null</code> is returned.
  
  @param indexName then name of the requested Solr index
  @return the Solr index configured with the given name