RFR: 8373638: RBTree public interface does not check all input parameters for validity

[David Holmes]

On Fri, 19 Dec 2025 11:05:45 GMT, Casper Norrbin <cnorrbin at openjdk.org> wrote:

> Hi everyone,
> 
> The public interface for the `RBTree` assumes most input is valid, and does not check for null pointers. This could lead to potential null pointer dereferences. We should instead assert to give clearer errors in debug builds and to avoid trying to dereference these null pointers.
> 
> Testing:
> - Oracle tiers 1-3

These all look like they would be good candidates for using `precond()`.

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PR Review: https://git.openjdk.org/jdk/pull/28922#pullrequestreview-3606606499