code: protected boolean checkImmutable(String resourceName) {
  
          boolean resourceImmutable = false;
          if (getImmutableResources().contains(resourceName)) {
              if (LOG.isDebugEnabled()) {
                  LOG.debug(
                      Messages.get().getBundle().key(Messages.LOG_IMPORTEXPORT_RESOURCENAME_IMMUTABLE_1, resourceName));
              }
              // this resource must not be modified by an import if it already exists
              String storedSiteRoot = getCms().getRequestContext().getSiteRoot();
              try {
                  getCms().getRequestContext().setSiteRoot("/");
                  getCms().readResource(resourceName);
                  resourceImmutable = true;
                  if (LOG.isDebugEnabled()) {
                      LOG.debug(
                          Messages.get().getBundle().key(Messages.LOG_IMPORTEXPORT_IMMUTABLE_FLAG_SET_1, resourceName));
                  }
              } catch (CmsException e) {
                  // resourceNotImmutable will be true
                  if (LOG.isDebugEnabled()) {
                      LOG.debug(
                          Messages.get().getBundle().key(
                              Messages.LOG_IMPORTEXPORT_ERROR_ON_TEST_IMMUTABLE_1,
                              resourceName),
                          e);
                  }
              } finally {
                  getCms().getRequestContext().setSiteRoot(storedSiteRoot);
              }
          }
          return resourceImmutable;
      }
docs: Checks if the resources is in the list of immutable resources.<p>
  
  @param resourceName the name of the resource
  
  @return <code>true</code> or <code>false</code>