private Version createVersion(
      ProjectHistory projectHistory,
      Project projectState,
      LogMessage logMessage,
      ACUser user,
      Version previousVersion)
      throws ESException {
    final Version newVersion = VersioningFactory.eINSTANCE.createVersion();

    long computedChecksum = ModelUtil.NO_CHECKSUM;

    try {
      if (ServerConfiguration.isComputeChecksumOnCommitActive()) {
        computedChecksum = ModelUtil.computeChecksum(projectState);
      }
    } catch (final SerializationException exception) {
      // TODO: clarify what to do in case checksum computation fails + provide ext. point
      throw new ESException(
          MessageFormat.format(
              Messages.VersionSubInterfaceImpl_ChecksumComputationFailed,
              projectHistory.getProjectName()),
          exception);
    }

    // newVersion.setChanges(changePackage);

    logMessage.setDate(new Date());
    logMessage.setAuthor(user.getName());
    newVersion.setLogMessage(logMessage);

    // latest version == getVersion.size() (version start with index 0 as
    // the list), branch from previous is used.
    newVersion.setPrimarySpec(
        Versions.createPRIMARY(
            previousVersion.getPrimarySpec(), projectHistory.getVersions().size()));
    newVersion.getPrimarySpec().setProjectStateChecksum(computedChecksum);
    newVersion.setNextVersion(null);

    projectHistory.getVersions().add(newVersion);
    return newVersion;
  }