[automerger skipped] Fix kotlin nullable errors in CredentialManager am:...

[automerger skipped] Fix kotlin nullable errors in CredentialManager am: b3198987 -s ours am: 1564c85e -s ours am: fcb44088 -s ours am: 2858f29f -s ours

am skip reason: Merged-In I9d45c775f6687a30e6e85e9ec3d9fc1944a2dd83 with SHA-1 ea28a7bf is already in history

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24719185



Change-Id: I292ef37711e89c89634cc8fa4dfe55b29b4b4517
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>