[jdk17u-dev] RFR: 8301989: new javax.swing.text.DefaultCaret().setBlinkRate(N) results in NPE

[Goetz Lindenmaier]

I backport this for parity with 17.0.15-oracle.

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Commit messages:
 - Backport e81f20b50405dc02963c8bf549000c60e78152d8

Changes: https://git.openjdk.org/jdk17u-dev/pull/3284/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=3284&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301989
  Stats: 49 lines in 2 files changed: 46 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/3284.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/3284/head:pull/3284

PR: https://git.openjdk.org/jdk17u-dev/pull/3284