code: def submissions
      page = @client.get_nokogiri @url
      @submissions ||= page.css('.gradeTable tbody tr').map { |tr|
        begin
          Stellar::Homework::Submission.new tr, self
        rescue ArgumentError
          nil
        end
      }.reject(&:nil?)
    end
docs: Creates a Stellar client scoped to an assignment.
  
   @param [URI, String] page_url URL to the assignment's main Stellar page
   @param [String] assignment name, e.g. "name"
   @param [Course] the course that issued the assignment
   List of submissions associated with this problem set.