message: Handle case where headSha is not in pr commits
diff: @@ -775,7 +775,7 @@ public class DefaultGitHubClient implements GitHubClient {
  prCommits.add(newCommit);
  }
  - if (StringUtils.isEmpty(pull.getHeadSha())) {
  + if (StringUtils.isEmpty(pull.getHeadSha()) || CollectionUtils.isEmpty(pull.getCommitStatuses())) {
  List<CommitStatus> commitStatuses = getCommitStatuses(lastCommitStatusObject);
  if (!CollectionUtils.isEmpty(commitStatuses)) {
  pull.setCommitStatuses(commitStatuses);
  