writer.write_timedelta_value("defaultDuration", self.default_duration)

def write_timedelta_value(self, key: Optional[str], value: Optional[timedelta]) -> None:
    if isinstance(value, timedelta):
        if key:
            self.writer[key] = str(value)  # <-- Incorrect format
        else:
            self.value = str(value)

from datetime import timedelta

from isodate import duration_isoformat
from kiota_abstractions.serialization.serialization_writer import SerializationWriter
from msgraph.generated.models.booking_service import BookingService


def patch_booking_service(booking_service: BookingService) -> None:
    old_serializer = booking_service.serialize

    def booking_service_serializer_patch(writer: SerializationWriter) -> None:
        old_serializer(writer)
        if isinstance(booking_service.default_duration, timedelta):
            writer.writer["defaultDuration"] = duration_isoformat(booking_service.default_duration) 

    booking_service.serialize = booking_service_serializer_patch 

from isodate import duration_isoformat

def write_iso8601_duration(self, key: Optional[str], value: Optional[timedelta]) -> None:
    """
    Writes a timedelta as an ISO 8601 duration string (e.g., P1DT2H3M4S).
    """
    if isinstance(value, timedelta):
        duration = duration_isoformat(value)
        if key:
            self.writer[key] = duration
        else:
            self.value = duration

@dataclass
class BookingService(Entity, Parsable):
    ...
    def serialize(self, writer: SerializationWriter) -> None:
        ...
        # Use the custom method for ISO 8601 durations
        if hasattr(writer, "write_iso8601_duration"):
            writer.write_iso8601_duration("defaultDuration", self.default_duration)
        else:
            writer.write_timedelta_value("defaultDuration", self.default_duration)  # Fallback