code: public String getSiteRoot() {
  
          if (m_internal && (m_siteRoot == null)) {
              m_siteRoot = OpenCms.getSiteManager().getSiteRoot(m_target);
              if (m_siteRoot == null) {
                  m_siteRoot = "";
              }
          }
          return m_siteRoot;
      }
docs: Return the site root if the target of this link is internal, or <code>null</code> otherwise.<p>
  
  @return the site root if the target of this link is internal, or <code>null</code> otherwise