RFR: 8313874 - JNI NewWeakGlobalRef throws exception for null arg [v2]

[Oli Gillespie]

> According to the JNI spec for NewWeakGlobalRef:
> 
>> Returns NULL if obj refers to null, or if obj was a weak global reference, or if the VM runs out of memory. If the VM runs out of memory, an OutOfMemoryError will be thrown.
> 
> The current behaviour is that `NewWeakGlobalRef(nullptr)` throws an OutOfMemoryError, which it should not.
> 
> (Thanks @dholmes-ora for confirming the issue and suggesting a fix.)

Oli Gillespie has updated the pull request incrementally with one additional commit since the last revision:

  Review feedback
  
  Move test case to existing test, use .not_null() for null check.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15188/files
  - new: https://git.openjdk.org/jdk/pull/15188/files/87ab7c9e..69ab3c4b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15188&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15188&range=00-01

  Stats: 52 lines in 4 files changed: 10 ins; 41 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15188.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15188/head:pull/15188

PR: https://git.openjdk.org/jdk/pull/15188