checkParameter(sinceId.isPresent(), "'since' reference cannot be found");
checkParameter(geogig.getRepository().commitExists(sinceId.get()),
"'since' reference does not resolve to a commit");
RevCommit sinceCommit = geogig.getRepository().getCommit(sinceId.get());
Optional<ObjectId> untilId = geogig.command(RevParse.class).setRefSpec(commits.get(1))
.call();
checkParameter(untilId.isPresent(), "'until' reference cannot be found");
checkParameter(geogig.getRepository().commitExists(untilId.get()),
"'until' reference does not resolve to a commit");
RevCommit untilCommit = geogig.getRepository().getCommit(untilId.get());