export data error, TypeError: bad operand type for abs(): 'NoneType'

**Describe the bug**
export COCO with Images

**To Reproduce**
Steps to reproduce the behavior:
1. export COCO with Images
2. error logs:

```
[2025-10-27 10:34:32,727] [core.utils.common::custom_exception_handler::97] [ERROR] 485516e2-2829-4896-895f-6a5577f564b8 bad operand type for abs(): 'NoneType'
Traceback (most recent call last):
File "/label-studio/.venv/lib/python3.13/site-packages/rest_framework/views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "/label-studio/.venv/lib/python3.13/site-packages/django/utils/decorators.py", line 48, in _wrapper
return bound_method(*args, **kwargs)
File "/label-studio/label_studio/data_export/api.py", line 206, in get
export_file, content_type, filename = DataExport.generate_export_file(
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
project, tasks, export_type, download_resources, request.GET, hostname=request.build_absolute_uri('/')
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/label-studio/label_studio/data_export/models.py", line 168, in generate_export_file
converter.convert(input_json, tmp_dir, output_format, is_dir=False)
~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/label-studio/.venv/lib/python3.13/site-packages/label_studio_sdk/converter/converter.py", line 259, in convert
self.convert_to_coco(
~~~~~~~~~~~~~~~~~~~~^
input_data, output_data, output_image_dir=image_dir, is_dir=is_dir
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
)
^
File "/label-studio/.venv/lib/python3.13/site-packages/label_studio_sdk/converter/converter.py", line 796, in convert_to_coco
xywh = self.rotated_rectangle(label)
File "/label-studio/.venv/lib/python3.13/site-packages/label_studio_sdk/converter/converter.py", line 1037, in rotated_rectangle
if abs(label_r) > 0:
~~~^^^^^^^^^
TypeError: bad operand type for abs(): 'NoneType'
[2025-10-27 10:34:32,779] [django.request::log_response::253] [ERROR] Internal Server Error: /api/projects/6/export
[2025-10-27 10:34:32,779] [django.request::log_response::253] [ERROR] Internal Server Error: /api/projects/6/export
[2025-10-27 10:34:32,781] [django.server::log_message::213] [ERROR] "GET /api/projects/6/export?exportType=COCO_WITH_IMAGES HTTP/1.1" 500 1948
[2025-10-27 10:34:32,781] [django.server::log_message::213] [ERROR] "GET /api/projects/6/export?exportType=COCO_WITH_IMAGES HTTP/1.1" 500 1948

```

**Expected behavior**
erport zip

**Screenshots**

**Environment (please complete the following information):**
- OS: docker
- Label Studio Version: 1.21.0