Error when replacing items

[mkw]

In lru-cache.js, the set function calls "this.get(key)" with no callback when replacing an item. At least in single user mode (possibly always) this will trigger an 'undefined is not a function' exception whenever an item is replaced.

To fix this, a check for the validity of the callback function should be added:

var LRUCacheProxy = function LRUCacheProxy(options) {
    if (!(this instanceof LRUCacheProxy)) {
        if(cluster.isMaster) {
            var lru = new LRUCache(options);
            var lruGet = LRUCache.prototype.get;

            lru.get = function(key, callback) {
                callback && callback(lruGet.apply(lru, arguments));
            };

            return lru;
        }

        return new LRUCacheProxy(options);
    }

    this.namespace = options.namespace || 'default';

    send(this.namespace, 'constructor', options, function() {});
};