code: public static void validateRollbackState(final String patchID, final InstalledIdentity identity) throws PatchingException {
          final Set<String> validHistory = processRollbackState(patchID, identity);
          if (patchID != null && !validHistory.contains(patchID)) {
              throw PatchLogger.ROOT_LOGGER.patchNotFoundInHistory(patchID);
          }
      }
docs: Validate the consistency of patches to the point we rollback.
  
  @param patchID the patch id which gets rolled back
  @param identity the installed identity
  @throws PatchingException