Backport to branch(3.9) : Fix NullPointerException when a client is misconfigured with digital signature

[feeblefakie]

This is an automated request for a manual backport of the following:

• Original PR: Fix NullPointerException when a client is misconfigured with digital signature #302
• Commit to backport: e5ba069

1. Resolve any conflicts that occur during the cherry-picking process.

git fetch origin &&
git checkout 3.9-pull-302 &&
git cherry-pick --no-rerere-autoupdate -m1 e5ba0695fb7d46c1894f987cda41f0efee6dfdf8

2. Push the changes.
3. Merge this PR after all checks have passed.

Thank you!