code: function ensureTag(cwd, tag) {
    if (tag === 'v0.0.0') {
      // There is no such thing (most likely)
      return null;
    }
  
    const tagFile = path.join(cwd, '.git', 'refs', 'tags', tag);
    try {
      return fs.readFileSync(tagFile);
    } catch (error) {
      if (error.code !== 'ENOENT') {
        throw error;
      }
      return fetchTag(cwd, tag);
    }
  }
docs: Ensure that a tag was fetched from the remote
  
  DotCI only fetches the ref that is currently being built.
  We need the last version tag to determine the changes.
  This checks if a tag exists locally. If it doesn't, it will
  fetch the tag from `origin`.