code: function handleCacheConfig (cacheConfig) {
  	if (!cacheConfig) {
  		return defaultCacheConfig;
  	}
  
  	// Must have valid type.
  	if (!cacheConfig.hasOwnProperty('type') || !CACHE_TYPES.hasOwnProperty(cacheConfig.type)) {
  		cacheConfig.type = CACHE_TYPES.persistent;
  	}
  
  	// If type is persistent, need persistentDir.
  	if (cacheConfig.type === CACHE_TYPES.persistent && !cacheConfig.hasOwnProperty('persistentDir')) {
  		cacheConfig.persistentDir = defaultCacheConfig.persistentDir;
  	}
  
  	// expirationTime must be an integer value
  	if (!cacheConfig.hasOwnProperty('expirationTime') || !Number.isInteger(cacheConfig.expirationTime)) {
  		cacheConfig.expirationTime = defaultCacheConfig.expirationTime;
  	}
  
  	return cacheConfig;
  }
docs: /* Helper for handleArgs: config.cache.