Converts param dicts to defaultdicts returning "None" on KeyError
Converts param dicts to defaultdicts returning "None" on KeyError

mitodl/ims_lti_py,harvard-dce/dce_lti_py,brainheart/dce_lti_py,bsulcer/ims_lti_py,nikolas/ims_lti_py,UbiCastTeam/ims_lti_py,tophatmonocle/ims_lti_py