code: function isMasterExternalValueOk(masterId, instances) {
          const instanceIds = Object.keys(instances);
          let instance;
          let hasExternal;
  
          for (let i = 0; i < instanceIds.length; i++) {
              instance = instances[instanceIds[i]];
              if (instance.external) {
                  hasExternal = true;
                  break;
              }
          }
  
          if (hasExternal) {
              return !!instances[masterId].external;
          }
  
          return true;
      }
docs: Checks that if there are external instances, the master is
  one of them
  
  @param {String} masterId  - Instance ID of master
  @param {Object} instances - Instances map
  
  @returns {Boolean} True if there are no external instances or
  if there are external instances and the master is
  one of them