Fixing small issues with get logic in formgrader.
Fixing small issues with get logic in formgrader.

jhamrick/nbgrader,dementrock/nbgrader,dementrock/nbgrader,jupyter/nbgrader,jhamrick/nbgrader,ellisonbg/nbgrader,jhamrick/nbgrader,jupyter/nbgrader,modulexcite/nbgrader,MatKallada/nbgrader,EdwardJKim/nbgrader,EdwardJKim/nbgrader,alope107/nbgrader,jhamrick/nbgrader,EdwardJKim/nbgrader,MatKallada/nbgrader,alope107/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader,EdwardJKim/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader,modulexcite/nbgrader,ellisonbg/nbgrader,jupyter/nbgrader