code: function (conf) {
          var slot, set;
          try {
              if (!conf.preserveId) {
                  conf = scrubConf(conf);
              }
              slot = Slot(conf);
              masterGroup.add(slot);
              if (slot.group) {
                  set = [].concat(slot.group);
                  set.forEach(function (groupName) {
                      var group = GroupFactory.create(groupName);
                      group.add(slot);
                  });
              }
          } catch (err) {
              log('error', {
                  conf: conf,
                  msg: err.message
              });
          } finally {
              return slot || null;
          }
      }
docs: ## create(options)
  @param {Object} conf
  @return {?Slot} Null on error.