should bookmark.id return nil

hey guys so i'm having issues adding a Like/Dislike function to my bookmarks on my page.

basically i have a snippet of code given to me that lives in my User model:

   def liked(bookmark)
     likes.where(bookmark_id: bookmark.id).first
   end

however when i am running the server and clicking on the topic to show the associated bookmarks, i keep getting the

undefined method `id' for nil:NilClass

my question is... firstly what is going wrong here? and secondly, whats the difference between bookmark_id and bookmark.id?

im pretty sure id doesn't exist for bookmark... and if not... how would i add it? ive tried via migration, unfortunately nothing great came from that