I have a Rails 6 app that uses Active Storage to store multiple images to a model (Activity) with `has_many_attached`. 

I don't understand how to append extra images instead of replacing the existing images. When I upload images the first time they save correctly. However, when I update the record, and I add a new image, the previous images are replaced by the new image. In Rails 5 the new image would be appended without replacing the previously saved images.

How do I append a new image instead of replacing the previous images?

I have an Activity model that has the following:

```
has_many_attached :images

```

In the form I have:

```
<%= f.file_field :images, multiple: true %>

```

In the controller I have the following:

```
def update
  @activity = Activity.find(params[:id])

  if @activity.update(activity_params)
    flash[:success] = "Saved"
    redirect_to activity_path(@activity)
  else
    flash[:error] = "Not saved"
    redirect_to edit_activity_path(@activity)
  end
end

private

  def activity_params
    params.require(:activity).permit(:name, images:[])
  end

```