RFR: 8377796: java.net.http.HttpClient.send() and sendAsync() never complete when BodyHandler.apply() returns null [v4]

[Jaikiran Pai]

> Can I please get a review of this change which proposes to address the issue noted in https://bugs.openjdk.org/browse/JDK-8377796?
> 
> The change here asserts that if `BodyHandler.apply()` returns `null`, then the HTTP request completes exceptionally. A new test has been introduced to reproduce the issue and verify the fix.

Jaikiran Pai has updated the pull request incrementally with one additional commit since the last revision:

  undo unintentional whitespace changes during merge conflict resolution

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29691/files
  - new: https://git.openjdk.org/jdk/pull/29691/files/a48f2948..9bafcab5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29691&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29691&range=02-03

  Stats: 71 lines in 1 file changed: 3 ins; 3 del; 65 mod
  Patch: https://git.openjdk.org/jdk/pull/29691.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29691/head:pull/29691

PR: https://git.openjdk.org/jdk/pull/29691