undefined method `synchronize' for nil:NilClass

Question

I just created a new app from scratch on rails4.0.0.rc1 with 1.9.3-p374 (which should work according to the guides).

However, I fail doing a simple create-action.

class Books
  def create
    @book = Book.new book_params

    if @book.save
      redirect_to @book
    else
      render action: :new
    end
  end

  private

  def book_params
    params.require(:book).permit(:name, :description)
  end
end

Doing a create here results a

undefined method `synchronize' for nil:NilClass

with the error pointing to the line of if @book.save.

Is that because of 1.9.3 or did I miss something?

Answer 1

Apparently, It was failing because of the friendlyId gem. If you use friendlyId, you may need to specify the rails4-branch.

gem 'friendly_id', github: 'FriendlyId/friendly_id', branch: 'rails4'

edit: Make sure to get the actual branch/version from norman/friendly_id. According to the readme, it needs to be at least branch: 5.0.0-beta to work with rails4.

edit2: now it is 5.0.0.rc2, as I said, make sure to get the actual branch/version, I won't obviously update this answer every time there is a version update. Also, read the comments to this answer, there are plenty of helpful information.

Answer 2

pduersteler's answer didn't work for me and failed with this error:

fatal: ambiguous argument 'rails4': unknown revision or path not in the working tree.

The README was update on Sep 23, 2013 with the following, which installed without error:

gem 'friendly_id', '5.0.0.rc2' # Note: You MUST use 5.0.0 or greater for Rails 4.0+