code: public CmsJspResourceWrapper getNavigationDefaultFile() {
  
          if (m_navigationDefaultFile == null) {
              if (isFolder()) {
                  try {
                      m_navigationDefaultFile = wrap(m_cms, m_cms.readDefaultFile(this, CmsResourceFilter.DEFAULT));
                  } catch (CmsSecurityException e) {
                      if (LOG.isDebugEnabled()) {
                          LOG.debug(e.getMessage(), e);
                      }
                  }
              }
          } else {
              m_navigationDefaultFile = this;
          }
          return m_navigationDefaultFile;
      }
docs: Returns the default resource for this resource.<p>
  
  If this resource is a file, then this file is returned.<p>
  
  Otherwise, in case this resource is a folder:<br>
  <ol>
  <li>the {@link CmsPropertyDefinition#PROPERTY_DEFAULT_FILE} is checked, and
  <li>if still no file could be found, the configured default files in the
  <code>opencms-vfs.xml</code> configuration are iterated until a match is
  found, and
  <li>if still no file could be found, <code>null</code> is returned
  </ol>
  
  @return the default file for the given folder
  
  @see CmsObject#readDefaultFile(CmsResource, CmsResourceFilter)