text: public virtual NGit.Api.RebaseCommand SetUpstream(string upstream){try{ObjectId upstreamId = repo.Resolve(upstream);if (upstreamId == null){throw new RefNotFoundException(MessageFormat.Format(JGitText.Get().refNotResolved, upstream));}upstreamCommit = walk.ParseCommit(repo.Resolve(upstream));upstreamCommitName = upstream;return this;}catch (IOException ioe){throw new JGitInternalException(ioe.Message, ioe);}}