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
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
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.