[Backport 2.x] Handle the audit config being null (opensearch-project…

…#4664)

Signed-off-by: Merlin <na@notaccessible.xyz>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

src/main/java/org/opensearch/security/securityconf/DynamicConfigFactory.java

@@ -82,6 +82,7 @@ public class DynamicConfigFactory implements Initializable, ConfigurationChangeL
     private static SecurityDynamicConfiguration<TenantV7> staticTenants = SecurityDynamicConfiguration.empty();
     private static final WhitelistingSettings defaultWhitelistingSettings = new WhitelistingSettings();
     private static final AllowlistingSettings defaultAllowlistingSettings = new AllowlistingSettings();
+    private static final AuditConfig defaultAuditConfig = AuditConfig.from(Settings.EMPTY);
 
     static void resetStatics() {
         staticRoles = SecurityDynamicConfiguration.empty();
@@ -323,7 +324,7 @@ public void onChange(Map<CType, SecurityDynamicConfiguration<?>> typeToConfig) {
         eventBus.post(whitelist == null ? defaultWhitelistingSettings : whitelist);
         eventBus.post(allowlist == null ? defaultAllowlistingSettings : allowlist);
         if (cr.isAuditHotReloadingEnabled()) {
-            eventBus.post(audit);
+            eventBus.post(audit == null ? defaultAuditConfig : audit);
         }
 
         initialized.set(true);