handle nil for feature flag check
handle nil for feature flag check

test plan
 - errors should go away from sentry

fixes FOO-1622
flag=granular_permissions_course_files

Change-Id: I2ac661f5080d3f0ad432f10802105ef09b196456
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/258991
Reviewed-by: Charley Kline <05950d7e90ba5e3da323378368c22b3ffaaf6647@instructure.com>
QA-Review: Charley Kline <05950d7e90ba5e3da323378368c22b3ffaaf6647@instructure.com>
Product-Review: Charley Kline <05950d7e90ba5e3da323378368c22b3ffaaf6647@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms