RFR: 8370467: BorderFactory.createBevelBorder and createSoftBevelBorder throws NPE for null highlight and shadow

[Prasanta Sadhukhan]

If we pass null as highlight and shadow color to `BorderFactory.createBevelBorder` and `createSoftBevelBorder`
it throws NPE which is not mentioned in the spec as the expected outcome.
Fixed the NPE and the spec

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Commit messages:
 - 8370467: BorderFactory.createBevelBorder and createSoftBevelBorder throws NPE for null highlight and shadow

Changes: https://git.openjdk.org/jdk/pull/27949/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27949&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370467
  Stats: 69 lines in 2 files changed: 66 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/27949.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27949/head:pull/27949

PR: https://git.openjdk.org/jdk/pull/27949