code: function attemptListIndexesFromVault(state, vault, topic, partialIndex, options, cb) {
  	// 0-length array response indicates non-existence in this vault
  	// this may be totally acceptable for volatile caches
  
  	if (!vault.archive.list) {
  		return state.error(null, 'List-operations not supported on vault ' + vault.name, cb);
  	}
  
  	var topicApi = configuration.getTopicApi(topic, vault.name);
  	if (!topicApi) {
  		// no API available for this topic on this vault
  
  		logger.verbose('No API available for topic', topic, 'on vault', vault.name);
  		return cb();
  	}
  
  	// check if there even is an index
  
  	if (!topicApi.index) {
  		return state.error(null, 'Cannot list indexes on a topic without an index signature', cb);
  	}
  
  	// attempt to get from the vault
  
  	logger.verbose('Attempting to list indexes for topic', topic, 'on vault', vault.name);
  
  	var startTime = process.hrtime();
  
  	vault.archive.list(topicApi, topic, partialIndex, options, function (error, indexes) {
  		if (error) {
  			exports.emit('vaultError', vault.name, 'list');
  
  			// alert the error and mark state as erroneous
  			var context = {
  				index: partialIndex,
  				operation: 'list',
  				topic: topic,
  				vault: vault.name
  			};
  
  			logger.alert.data(context).log(error);
  
  			return state.error(null, null, cb);
  		}
  
  		exports.emit('operation', vault.name, 'list', process.hrtime(startTime));
  
  		// value should be undefined to indicate a valid case of non-existing value
  
  		logger.verbose('Found', indexes.length, 'indexes in vault', vault.name);
  
  		cb(null, indexes);
  	});
  }
docs: vault access helpers for the Archivist class --------------------------------------------