uninitialized constant Prawn::Core

[exocode]

Hi,

sorry short question:

I try to implement your form gem into my existing Bill < Prawn::Document. Prawn is installed correctly and is rendering my PDF.

Now I added gem 'prawn-blank' to my gemfile and try to use the form like this:

require "prawn"
require "prawn/blank"

Bill < Prawn::Document

def render_bill
    text_field(
        :at => [200,55],
        :name=>"text",
        :value=>"Try edit me!"
    )
end
end

# in controller

respond_to do |format|
          format.pdf do
            pdf = Bill.new(current_user, bill)
            send_data pdf.render,
                      type: "application/pdf",
                      disposition: "inline"
          end
        end


What I am doing wrong? Thank you!