microsoft.graph.onPremisesPublishing wrong serialization

Start with the generated Application and OnPremisesPublishing models and the JsonSerializationWriter used in the reproduction. Run the provided serialization example and compare its onPremisesPublishing output with the additional_data workaround. Done means the SDK emits JSON accepted by the backend and the patch request no longer returns InvalidJson_BadRequest.

Describe the bug

Same bug as in the PHP SDK from 2025

https://github.com/microsoftgraph/msgraph-beta-sdk-php/issues/356

from msgraph_beta import GraphServiceClient as BetaClient
from msgraph_beta.generated.models.application import Application as Application
from msgraph_beta.generated.models.on_premises_publishing import OnPremisesPublishing
from msgraph_beta.generated.models.external_authentication_type import ExternalAuthenticationType

request_body = Application(
    on_premises_publishing = OnPremisesPublishing(
        external_authentication_type=ExternalAuthenticationType.Passthru,
        internal_url="http://localhost:65001",
        external_url="https://whatever",
        is_http_only_cookie_enabled=False,
        is_on_prem_publishing_enabled=True,
        is_persistent_cookie_enabled=False,
        is_secure_cookie_enabled=False,
        is_state_session_enabled=False,
        is_translate_host_header_enabled=False,
        is_translate_links_in_body_enabled=False,
        is_backend_certificate_validation_enabled=False
    ),
)

from kiota_serialization_json.json_serialization_writer import JsonSerializationWriter
writer = JsonSerializationWriter()
request_body.serialize(writer)
print(writer.get_serialized_content().decode('utf-8'))

Output:

{"@odata.type": "#microsoft.graph.application", "onPremisesPublishing": {"externalAuthenticationType": "passthru", "externalUrl": "https://whatever", "internalUrl": "http://localhost:65001", "isBackendCertificateValidationEnabled": false, "isHttpOnlyCookieEnabled": false, "isOnPremPublishingEnabled": true, "isPersistentCookieEnabled": false, "isSecureCookieEnabled": false, "isStateSessionEnabled": false, "isTranslateHostHeaderEnabled": false, "isTranslateLinksInBodyEnabled": false}}

await beta_client.applications.by_application_id(app.application.id).patch(request_body) then fails with

        APIError
        Code: 400
        message: None
        error: MainError(additional_data={}, code='InvalidJson_BadRequest', details=None, inner_error=InnerError(additional_data={}, client_request_id='xxxx', date=datetime.datetime(2026, 7, 10, 8, 49, 27), odata_type=None, request_id='xxxx'), message='Valid JSON content expected.', target=None)

Expected behavior

proper error message and properly serialized data sent to the backend

How to reproduce

see above

SDK Version

1.59.0

Latest version known to work for scenario above?

No response

Known Workarounds

        request_body = BetaApplication(
            additional_data = {
                "microsoft.graph.onPremisesPublishing": {
                    "@odata.type": "#microsoft.graph.onPremisesPublishing",
                    "externalAuthenticationType": "passthru",
                    "internalUrl": "http://localhost:65001",
                    "externalUrl": EXTERNAL_URL,
                    "isHttpOnlyCookieEnabled": False,
                    "isOnPremPublishingEnabled": True,
                    "isPersistentCookieEnabled": False,
                    "isSecureCookieEnabled": False,
                    "isStateSessionEnabled": False,
                    "isTranslateHostHeaderEnabled": False,
                    "isTranslateLinksInBodyEnabled": False,
                    "isBackendCertificateValidationEnabled": False
                }
            }
        )

Debug output

No response

Configuration

No response

Other information

No response