lib/memory.js
function (key, done) {
      var val = null;
      if(cache.hasOwnProperty(key)) {
        val = cache[key];
      }
      return done(null, val);
    }
function (key, done) {
      var val = null;
      if(cache.hasOwnProperty(key)) {
        val = cache[key];
      }
      return done(null, val);
    }
Attempt to retrieve the set value for the given key.
@param {string} key
@param {function} done