code: function(conversationId, participants, callback) {
        conversationId = utils.toUUID(conversationId);
        if (!conversationId) return callback(new Error(utils.i18n.conversations.id));
        if (!utils.isArray(participants)) return callback(new Error(utils.i18n.conversations.participants));
        utils.debug('Conversation addParticipants: ' + conversationId);
  
        var operations = participants.map(function(participant) {
          return {
            operation: 'add',
            property: 'participants',
            value: participant
          };
        });
  
        edit(conversationId, operations, callback);
      }
docs: Participants add/remove/set operations on a conversation
  
  @param  {String}   conversationId  Conversation UUID
  @param  {Object}   participants    Array of participant IDs
  @param  {Function} callback        Callback function