Error when a secret doesn't have an annotation.  As a workaround I added a dummy annotation to all my secrets, i.e.

kubectl annotate secret --all jenkins.io/foo=bar

Issue seems to be here not checking that annotations can be null https://github.com/jenkinsci/kubernetes-credentials-provider-plugin/blob/82b67a06d24b8cc500856e46f3328337e58a63ca/src/main/java/com/cloudbees/jenkins/plugins/kubernetes_credentials_provider/SecretUtils.java#L186