code: public boolean isDefaultUser(String userName) {
  
          if (CmsStringUtil.isEmptyOrWhitespaceOnly(userName)) {
              return false;
          }
  
          // first check without ou prefix, to stay backwards compatible
          boolean isDefault = m_userAdmin.equals(userName);
          isDefault = isDefault || m_userGuest.equals(userName);
          isDefault = isDefault || m_userExport.equals(userName);
          isDefault = isDefault || m_userDeletedResource.equals(userName);
  
          // now check with ou prefix
          isDefault = isDefault || userName.equals(CmsOrganizationalUnit.SEPARATOR + m_userAdmin);
          isDefault = isDefault || userName.equals(CmsOrganizationalUnit.SEPARATOR + m_userGuest);
          isDefault = isDefault || userName.equals(CmsOrganizationalUnit.SEPARATOR + m_userExport);
          isDefault = isDefault || userName.equals(CmsOrganizationalUnit.SEPARATOR + m_userDeletedResource);
  
          return isDefault;
      }
docs: Checks if a given user name is the name of one of the OpenCms default users.<p>
  
  @param userName the group name to check
  
  @return <code>true</code> if user name is one of OpenCms default users, <code>false</code> if it is not
  or if <code>userName</code> is <code>null</code> or an empty string (no trim)
  
  @see #getUserAdmin()
  @see #getUserExport()
  @see #getUserGuest()
  @see #getUserDeletedResource()