Rails 4 Unpermitted Parameters for Array

I have an array field in my model and I'm attempting to update it.

My strong parameter method is below

def post_params
  params["post"]["categories"] = params["post"]["categories"].split(",")

  params.require(:post).permit(:name, :email, :categories)
end

My action in my controller is as follows

def update
  post = Post.find(params[:id]

  if post and post.update_attributes(post_params)
    redirect_to root_url
  else
    redirect_to posts_url
  end
end

However, whenever I submit the update the post, in my development log I see

Unpermitted parameters: categories

The parameters passed through is

  Parameters: {"utf8"=>"✓", "authenticity_token"=>"auth token", "id"=>"10", 

"post"=>{"name"=>"Toni Mitchell", "email"=>"eileen_hansen@hayetokes.info", "categories"=>",2"}}

I want to think it has something to do with the fact that the attribute categories is an array since everything else looks fine. Then again, I could be wrong. So, what's wrong with my code and why is not letting me save the categories field when clearly it is permitted to do so? Thanks.

Try this

params.require(:post).permit(:name, :email, :categories => [])

(Disregard my comment, I don't think that matters)