RFR: 8377910: Minor cleanup of java/io/FileDescriptor/Sharing.java [v3]

[Brian Burkhalter]

> Null checks potentially mask a more serious, fundamental problem and should be removed to allow a `NullPointerException` to be throw if the variable is `null`.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8377910: Fix indentation and make java.io imports explicit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29718/files
  - new: https://git.openjdk.org/jdk/pull/29718/files/9dd1613c..73d9aeba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29718&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29718&range=01-02

  Stats: 37 lines in 1 file changed: 7 ins; 0 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/29718.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29718/head:pull/29718

PR: https://git.openjdk.org/jdk/pull/29718