code: def add(*items)
        items = items.flatten.parse_objects
        return @collection if items.empty?
  
        notify_will_change!
        additions_will_change!
        removals_will_change!
        # take all the items
        items.each do |item|
          @additions.push item
          @collection.push item
          #cleanup
          @removals.delete item
        end
        @collection
      end
docs: Add Parse::Objects to the relation.
   @overload add(parse_object)
    Add a Parse::Object or Parse::Pointer to this relation.
    @param parse_object [Parse::Object,Parse::Pointer] the object to add
   @overload add(parse_objects)
    Add an array of Parse::Objects or Parse::Pointers to this relation.
    @param parse_objects [Array<Parse::Object,Parse::Pointer>] the array to append.
   @return [Array<Parse::Object>] the collection