How to check if a user has voted before 24hrs rails 4

I need to check whether the user has voted before 24 hours if yes I need to allow him to vote

if current_user.vote = true
  if @vote.updated_at > Time.now - 24.hours          
    @vote.save          
  end
end

but I am getting error as undefined method `>' for nil:NilClass So how can I fix this?