final String commitMessage = this.message == null ? "" : this.message;
RevCommit unnnamedCommit = new RevCommitImpl(ObjectId.NULL, treeId, parentIds, author,
committer, commitMessage);
ObjectId commitId = new HashObject().setObject(unnnamedCommit).call();
return new RevCommitImpl(commitId, treeId, parentIds, author, committer, commitMessage);
}