RFR: 8346094: Harden X509CertImpl.getExtensionValue for NPE cases

[Sean Coffey]

On Mon, 27 Jan 2025 12:39:45 GMT, Konanki Sreenath <duke at openjdk.org> wrote:

> Earlier code will trigger NPE if the certificate does not contain the extensions or if the requested extensions does not exist. The better approach for hardening **getExtensionValue** here is to to check for NULL explicitly before calling **getExtensionValue()** and avoding try-catch block which ensures the readability and maintainability.
> 
> After scanning in multiple places where invokng getExtensions on the X509CertInfo reference, the check for NULL is added in the **getKeyUsage()** as well while calling before **getExtensionValue()**
> 
> The associated tests are written and added in test class **CertificateExtensions**. Which will ensure to validate the 
> **getExtensionValue()** and **getKeyUsage()** methods in **X509CertImpl** class.

LGTM

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Marked as reviewed by coffeys (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/23315#pullrequestreview-2598972284