Fix exception thrown when JSON can't be decoded.

[TheNewSound]

It currently crashes with a TypeError when using property_exists($object, "...") because $object is null if the JSON can't be decoded:

TypeError
vendor/invoiceninja/sdk-php/src/Exceptions/ApiException.php:37

property_exists(): Argument #1 ($object_or_class) must be of type object|string, null given


Stack trace:

InvoiceNinja\Sdk\Exceptions\ApiException property_exists()

vendor/invoiceninja/sdk-php/src/Exceptions/ApiException.php:37

InvoiceNinja\Sdk\Exceptions\ApiException::parseResponseBody()

vendor/invoiceninja/sdk-php/src/Exceptions/ApiException.php:37

InvoiceNinja\Sdk\Exceptions\ApiException::createFromResponse()

vendor/invoiceninja/sdk-php/src/Exceptions/ApiException.php:19

[turbo124]

Thanks!