Make exception handling experience intuitive

I'm encoutering an issue with using ApiException to get exceptions in v2.0.0 RC9. The message variable is always blank with exceptions for most commands regarding working with sites, drives, and files. The exception is in there, just buried inside of a private 'error' variable.

Example of getting a site that doesn't exist:

<?php

error_reporting(E_ALL);
ini_set('display_errors', '1');

require_once __DIR__ . '/vendor/autoload.php';

use Microsoft\Graph\Generated\Models;
use Microsoft\Graph\GraphRequestAdapter;
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Kiota\Authentication\Oauth\ClientCredentialContext;
use Microsoft\Kiota\Authentication\PhpLeagueAuthenticationProvider;

try {
    $tokenRequestContext = new ClientCredentialContext(
        $tenantId,
        $clientId,
        $clientSecret
    );
    $scopes = ['https://graph.microsoft.com/.default'];
    $authProvider = new PhpLeagueAuthenticationProvider($tokenRequestContext, $scopes);
    $requestAdapter = new GraphRequestAdapter($authProvider);
    $graphServiceClient = new GraphServiceClient($requestAdapter);

    /** @var Models\Site $site  */
    $site = $graphServiceClient->sitesById($siteId)->get()->wait();
} catch (ApiException $ex) {
    echo $ex->getMessage();
}

?>

This returns the a blank $ex->message, and the following var_dump($ex):

object(Microsoft\Graph\Generated\Models\ODataErrors\ODataError)#59 (9) {
  ["message":protected]=>
  string(0) ""
  ["string":"Exception":private]=>
  string(0) ""
  ["code":protected]=>
  int(0)
  ["file":protected]=>
  string(131) "/home/username/test/vendor/microsoft/microsoft-graph/src/Generated/Models/ODataErrors/ODataError.php"
  ["line":protected]=>
  int(37)
  ["trace":"Exception":private]=>
  array(7) {
    [0]=>
    array(5) {
      ["file"]=>
      string(114) "/home/username/test/vendor/microsoft/kiota-serialization-json/src/JsonParseNode.php"
      ["line"]=>
      int(107)
      ["function"]=>
      string(28) "createFromDiscriminatorValue"
      ["class"]=>
      string(55) "Microsoft\Graph\Generated\Models\ODataErrors\ODataError"
      ["type"]=>
      string(2) "::"
    }
    [1]=>
    array(5) {
      ["file"]=>
      string(114) "/home/username/test/vendor/microsoft/kiota-http-guzzle/src/GuzzleRequestAdapter.php"
      ["line"]=>
      int(308)
      ["function"]=>
      string(14) "getObjectValue"
      ["class"]=>
      string(48) "Microsoft\Kiota\Serialization\Json\JsonParseNode"
      ["type"]=>
      string(2) "->"
    }
    [2]=>
    array(5) {
      ["file"]=>
      string(114) "/home/username/test/vendor/microsoft/kiota-http-guzzle/src/GuzzleRequestAdapter.php"
      ["line"]=>
      int(88)
      ["function"]=>
      string(19) "throwFailedResponse"
      ["class"]=>
      string(41) "Microsoft\Kiota\Http\GuzzleRequestAdapter"
      ["type"]=>
      string(2) "->"
    }
    [3]=>
    array(5) {
      ["file"]=>
      string(99) "/home/username/test/vendor/php-http/promise/src/FulfilledPromise.php"
      ["line"]=>
      int(35)
      ["function"]=>
      string(30) "Microsoft\Kiota\Http\{closure}"
      ["class"]=>
      string(41) "Microsoft\Kiota\Http\GuzzleRequestAdapter"
      ["type"]=>
      string(2) "->"
    }
    [4]=>
    array(5) {
      ["file"]=>
      string(114) "/home/username/test/vendor/microsoft/kiota-http-guzzle/src/GuzzleRequestAdapter.php"
      ["line"]=>
      int(98)
      ["function"]=>
      string(4) "then"
      ["class"]=>
      string(29) "Http\Promise\FulfilledPromise"
      ["type"]=>
      string(2) "->"
    }
    [5]=>
    array(5) {
      ["file"]=>
      string(135) "/home/username/test/vendor/microsoft/microsoft-graph/src/Generated/Sites/Item/SiteItemRequestBuilder.php"
      ["line"]=>
      int(277)
      ["function"]=>
      string(9) "sendAsync"
      ["class"]=>
      string(41) "Microsoft\Kiota\Http\GuzzleRequestAdapter"
      ["type"]=>
      string(2) "->"
    }
    [6]=>
    array(5) {
      ["file"]=>
      string(64) "/home/username/test/graph-bug.php"
      ["line"]=>
      int(32)
      ["function"]=>
      string(3) "get"
      ["class"]=>
      string(59) "Microsoft\Graph\Generated\Sites\Item\SiteItemRequestBuilder"
      ["type"]=>
      string(2) "->"
    }
  }
  ["previous":"Exception":private]=>
  NULL
  ["additionalData":"Microsoft\Graph\Generated\Models\ODataErrors\ODataError":private]=>
  array(0) {
  }
  ["error":"Microsoft\Graph\Generated\Models\ODataErrors\ODataError":private]=>
  object(Microsoft\Graph\Generated\Models\ODataErrors\MainError)#80 (6) {
    ["additionalData":"Microsoft\Graph\Generated\Models\ODataErrors\MainError":private]=>
    array(1) {
      ["innerError"]=>
      array(3) {
        ["date"]=>
        string(19) "2022-10-17T16:23:06"
        ["request-id"]=>
        string(36) "80ddeda1-e38d-41fc-a42d-6e943d3b16cd"
        ["client-request-id"]=>
        string(36) "7ee8f8ec-2bd6-4609-aa90-3a2356efa61f"
      }
    }
    ["code":"Microsoft\Graph\Generated\Models\ODataErrors\MainError":private]=>
    string(12) "itemNotFound"
    ["details":"Microsoft\Graph\Generated\Models\ODataErrors\MainError":private]=>
    NULL
    ["innererror":"Microsoft\Graph\Generated\Models\ODataErrors\MainError":private]=>
    NULL
    ["message":"Microsoft\Graph\Generated\Models\ODataErrors\MainError":private]=>
    string(33) "Requested site could not be found"
    ["target":"Microsoft\Graph\Generated\Models\ODataErrors\MainError":private]=>
    NULL
  }
}

Empieza por Generated/Models/ODataErrors/ODataError.php y MainError, y luego sigue el fallo a través de GuzzleRequestAdapter::throwFailedResponse y SiteItemRequestBuilder.php. Reproduce el mensaje que falta con el ejemplo sitesById(...)->get()->wait(). Se considera completado cuando el mensaje de error de la API está disponible mediante ApiException::getMessage().