RFR: 8254876: (fs) NullPointerException not thrown when first argument to Path.of or Paths.get is null

[Brian Burkhalter]

Please review this simple fix to have Path.of(String,String) throw a NullPointerException if the first parameter is null.

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Commit messages:
 - 8254876: (fs) NullPointerException not thrown when first argument to Path.of or Paths.get is null

Changes: https://git.openjdk.java.net/jdk/pull/1020/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1020&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254876
  Stats: 14 lines in 3 files changed: 12 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1020.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1020/head:pull/1020

PR: https://git.openjdk.java.net/jdk/pull/1020