[jdk11u-dev] RFR: 8263940: NPE when creating default file system when default file system provider is packaged as JAR file on class path

[Amos Shi]

Backport of [JDK-8263940](https://bugs.openjdk.org/browse/JDK-8263940)
- to add details on diff

Testing
- Local: `SetDefaultProvider.java` - Test results: passed: 1
- Pipeline: 
- Testing Machine:

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Commit messages:
 - 8263940: Fix compile errors on Java 11
 - Backport 717792c3b728584413572e7aede83290779be2a2

Changes: https://git.openjdk.org/jdk11u-dev/pull/2647/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2647&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8263940
  Stats: 74 lines in 2 files changed: 66 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2647.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2647/head:pull/2647

PR: https://git.openjdk.org/jdk11u-dev/pull/2647