Prismic and Ruby on rails : undefined method `[]' for nil:NilClass when trying to get data from prismic api

I'm quite new to ruby and prismic. I'm trying to connect on the controller of my ruby on rails project to the prismic api.

their tutorial show the following code :

api = Prismic.api('https://your-repo-name.prismic.io/api')
doc = api.query(Prismic::Predicates.at("document.type", "page"))
content = doc.results

i installed the prismic gem correctly and put my repo name correctly. When i run my code, i get the following error :

NoMethodError in PageController#page
undefined method `[]' for nil:NilClass

for the line

doc = api.query(Prismic::Predicates.at("document.type", "page"))

I checked the api variable value and i get #<Prismic::API:0x007fbcaaab6418> in my api variable, so i guess it's working fine. I tried to change the predicates but it's doesn't change anything.

If you know a way to solve this problem i would be very gratefull. Thanks.

edit: my controller page where the error occurs :

Class PageController < ApplicationController
  def page

    api = Prismic.api('https://xxx.prismic.io/api')
    puts 'api ='
    puts api
    puts '==was api'
    doc = api.query(Prismic::Predicates.at("document.tags", ["conseil"]))
    content = doc.results

    puts 'content'
    @test1 = 'test'#content[0]['id']

  end
end