RFR: 8364751: ConstantBootstraps.explicitCast contradictory specification for null-to-primitive

[Roger Riggs]

On Sun, 10 Aug 2025 01:11:43 GMT, Chen Liang <liach at openjdk.org> wrote:

> ConstantBootstraps.explicitCast behaves like a snippet of code in its specification. However, in the rest of the nominal spec, it incorrectly assumes a null `value` and a primitive `dstType` results in a ClassCastException instead of the zero value of that primitive type. This is inconsistent with that snippet and the actual code behavior.
> 
> The specification is fixed, the test for `explicitCast` is merged into the main `ConstantBootstraps` test, and a new unit test case for `value = null` and `dstType = char.class` is added, verifying the outcome is `'u0000'`.

Looks ok; but another reviewer more familiar with the domain may be good.

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

Marked as reviewed by rriggs (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26714#pullrequestreview-3129796141