[jdk11u-dev] RFR: 8277224: sun.security.pkcs.PKCS9Attributes.toString() throws NPE

[Martin Doerr]

Clean backport of JDK-8277224.

-------------

Commit messages:
 - Backport 6bb04626af6574ef1e8d4b7dad0389d4b59f5d08

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/651/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=651&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277224
  Stats: 16 lines in 2 files changed: 11 ins; 2 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/651.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/651/head:pull/651

PR: https://git.openjdk.java.net/jdk11u-dev/pull/651