code: function readRebaseMetadataFile(fileName, continueOnError) {
      return fse.readFile(
        path.join(repository.path(), "rebase-merge", fileName),
        { encoding: "utf8" }
      )
        .then(fp.trim)
        .catch(function(err) {
          if (continueOnError) {
            return null;
          }
          throw err;
        });
    }
docs: /* In the case of FF merges and a beforeFinishFn, this will fail
  when looking for 'rewritten' so we need to handle that case.