RFR: 8370467: BorderFactory.createBevelBorder and createSoftBevelBorder throws NPE for null highlight and shadow [v6]

[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

Prasanta Sadhukhan has updated the pull request incrementally with two additional commits since the last revision:

 - javadoc update
 - javadoc update

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27949/files
  - new: https://git.openjdk.org/jdk/pull/27949/files/d8de38b3..27ed5b21

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27949&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27949&range=04-05

  Stats: 16 lines in 2 files changed: 16 ins; 0 del; 0 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