code: public String storeExternalLink(String externalLink) {
  
          if (!CmsStringUtil.isEmptyOrWhitespaceOnly(m_linkGallery)) {
              m_externalLinks.add(externalLink);
              return getExternalLinkFile(externalLink);
          }
  
          return null;
      }
docs: Add a new external link to the storage of external links.<p>
  
  All links in this storage are later used to create entries in the external link gallery.<p>
  
  @param externalLink link to an external resource
  
  @return the complete path to the external link file, if one is created.