[foreign-memaccess+abi] RFR: 8301806: TestNulls does not cover all API classes

[Maurizio Cimadamore]

On Fri, 10 Feb 2023 16:35:46 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> The TestNulls test does not cover the following API classes: Linker.Option, PaddingLayout, StructLayout, UnionLayout.
> 
> This patch adds coverage, and fixes several places where we weren't checking for `null`.

Marked as reviewed by mcimadamore (Committer).

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PR: https://git.openjdk.org/panama-foreign/pull/787