code: protected List<String> getImmutableResources() {
  
          if (m_immutables == null) {
              // get list of immutable resources
              m_immutables = OpenCms.getImportExportManager().getImmutableResources();
              if (m_immutables == null) {
                  m_immutables = Collections.emptyList();
              }
              if (LOG.isDebugEnabled()) {
                  LOG.debug(
                      Messages.get().getBundle().key(
                          Messages.LOG_IMPORTEXPORT_IMMUTABLE_RESOURCES_SIZE_1,
                          Integer.toString(m_immutables.size())));
              }
          }
          return m_immutables;
      }
docs: Returns the list of immutable resources.<p>
  
  @return the list of immutable resources