fix api doc typo and make optional consistent

fixes CNVS-13259

test plan
 - api docs should generate

Change-Id: I9d0a4cc5da86ef279ca4a4e30abbf43a70031788
Reviewed-on: https://gerrit.instructure.com/35349
Reviewed-by: Nick Cloward <ncloward@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>