[jdk11u-dev] RFR: 8273826: Correct Manifest file name and NPE checks

[Goetz Lindenmaier]

I backport this for parity with 11.0.14-oracle.

I had to do a few minor adaptions:

Resolve JarFile.java due to context.

Fix the test to run in the jdk11u environment.
Also, I changed an argument to newFileSystem() form 
Collections.emptyMap() to null. This factory method
internally uses emptyMap(), so the result is the same.

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Commit messages:
 - Backport 03a8d342b86e720d3cba08d540182b4ab161fba3

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/503/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=503&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8273826
  Stats: 139 lines in 5 files changed: 128 ins; 2 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/503.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/503/head:pull/503

PR: https://git.openjdk.java.net/jdk11u-dev/pull/503