[jdk11u-dev] RFR: 8233565: [TESTBUG] NullModalityDialogTest.java fails on MacOS

[Joshua Cao]

Not a clean backport:
* conflict in copyright year
* removing the test from ProblemList.txt is not clean because surrounding lines are different

Passes NullModalityDialogTest.java

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Commit messages:
 - 8233565: [TESTBUG] NullModalityDialogTest.java fails on MacOS

Changes: https://git.openjdk.org/jdk11u-dev/pull/1392/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=1392&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8233565
  Stats: 7 lines in 2 files changed: 3 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/1392.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev pull/1392/head:pull/1392

PR: https://git.openjdk.org/jdk11u-dev/pull/1392