code: function (cb) {
        async.map(self._repos, function (repo, repoCb) {
          self._client.gitdata.getReference({
            user: self._repoParts[repo].org,
            repo: self._repoParts[repo].repo,
            ref: branchDestFull
          }, function (err, res) {
            // Allow not found.
            if (err && err.code === NOT_FOUND) {
              repoCb(null, {
                repo: repo,
                exists: false,
                sha: null
              });
              return;
            }
  
            // Real error.
            if (self._checkAndHandleError(err, "branch.getDestRefs - " + repo, repoCb)) {
              return;
            }
  
            // Error if existing branches are not allowed.
            var sha = res.object.sha;
            if (!self._allowExisting) {
              self._checkAndHandleError(
                new Error("Found existing dest branch in repo: " + repo + " with sha: " + sha),
                null,
                repoCb);
              return;
            }
  
            // Have an allowed, existing branch.
            repoCb(null, {
              repo: repo,
              exists: true,
              sha: sha
            });
          });
        }, cb);
      }
docs: Check if the destination branches exist.