code: function (key, callback) {
          assertType(callback, Function);
  
          var index = this.indexOfKey(key);
  
          if (index >= 0) {
              callback(this.slot.values[index]);
              return true;
          }
  
          return false;
      }
docs: Gets the value associated with the specified key.
  @param {Object} key The key whose value to get.
  @param {Function} callback When this method returns, callback method is called with the value
  associated with the specified key, if the key is found; otherwise, null for the type of the value parameter.
  @returns {Boolean}