[jdk17u] RFR: 8277224: sun.security.pkcs.PKCS9Attributes.toString() throws NPE

[Sean Coffey]

Clean port of JDK-8277224

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Commit messages:
 - Backport 6bb04626af6574ef1e8d4b7dad0389d4b59f5d08

Changes: https://git.openjdk.java.net/jdk17u/pull/290/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=290&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/jdk17u/pull/290.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/290/head:pull/290

PR: https://git.openjdk.java.net/jdk17u/pull/290