[jdk21u-dev] RFR: 8343622: AesDkCrypto.stringToKey should not return null

[Goetz Lindenmaier]

I backport this for parity with 21.0.11-oracle

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Commit messages:
 - Backport ca46c3a5ba324ceb4f30df772cb73a673647323e

Changes: https://git.openjdk.org/jdk21u-dev/pull/2550/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2550&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343622
  Stats: 70 lines in 6 files changed: 54 ins; 11 del; 5 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2550.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2550/head:pull/2550

PR: https://git.openjdk.org/jdk21u-dev/pull/2550