Updated `getService` to check whether `getProvider` returns null when checking for preferred providers and `continue` the loop if that is the case. Added `NullPreferredList` test.
------------- Commit messages: - Fixed and renamed test, getService now continues loop instead of returning null - added test file Changes: https://git.openjdk.org/jdk/pull/18746/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18746&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8328864 Stats: 46 lines in 3 files changed: 45 ins; 1 del; 0 mod Patch: https://git.openjdk.org/jdk/pull/18746.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/18746/head:pull/18746 PR: https://git.openjdk.org/jdk/pull/18746
