code: function (key, value, def) {
                          if (! this.has(key)) {
                              this.put(key, value, def);
                              return true;
                          }
  
                          return false;
                      }
docs: Add an item to storage if it doesn't already exist
  
  @public
  
  @param  {Mixed}  key    The key to add
  @param  {Mixed}  value  The value to add
  @param  {Mixed}  def    The default to pass to function if doesn't already exist
  
  @return {Boolean}