AXIAM PHP SDK

Everywhere else on the §27 surface a PHP null property means "absent" and is left out of the wire body. A handful of fields need the third state, and only those declare T|JsonNull|null:

• UpdateDirectoryConfig::$groupBaseDn / $groupFilter (§30.2): null leaves the stored value alone, JsonNull::Null sends null and clears it — new UpdateDirectoryConfig(groupFilter: JsonNull::Null) sends exactly {"group_filter": null}.
• UpdateFederationConfigRequest's ten clearable members (§27.15 note 8, contract 1.60): $metadataUrl, $idpSigningCertPem, $idpMetadataSigningCertPem, $providerSlug, $authorizationEndpoint, $tokenEndpoint, $userinfoEndpoint, $appleTeamId, $appleKeyId and $buttonIcon. null leaves the stored value unchanged; new UpdateFederationConfigRequest(buttonIcon: JsonNull::Null) sends exactly {"button_icon": null} and clears it.
• SamlIdpInfo::$activeCredentialId / $nextCredentialId (§29.8 test 8): decoded as JsonNull::Null when the server said null (the slot is empty), and as PHP null only when it sent no such member.