code: function logClient (logClient) {
      if (defined(logClient)) {
          // validate that log client has required methods
          requireValidLogClient(logClient)
          // set default
          immutable.defaultLogClient = logClient
          // return immutable
          return ImmutableCore
      }
      // return default value
      return immutable.defaultLogClient
  }
docs: @function logClient
  
  get/set the default log client
  
  @param {object} logClient
  
  @returns {ImmutableCore|object}
  
  @throws {Error} on invalid logClient