COCO export failed

```
Traceback (most recent call last):
File "C:\Users\Deltra\anaconda3\lib\site-packages\rest_framework\views.py", line 506, in dispatch
response = handler(request, *args, **kwargs)
File "C:\Users\Deltra\anaconda3\lib\site-packages\django\utils\decorators.py", line 43, in _wrapper
return bound_method(*args, **kwargs)
File "C:\Users\Deltra\anaconda3\lib\site-packages\label_studio\data_export\api.py", line 183, in get
export_stream, content_type, filename = DataExport.generate_export_file(
File "C:\Users\Deltra\anaconda3\lib\site-packages\label_studio\data_export\models.py", line 161, in generate_export_file
converter.convert(input_json, tmp_dir, output_format, is_dir=False)
File "C:\Users\Deltra\anaconda3\lib\site-packages\label_studio_converter\converter.py", line 212, in convert
self.convert_to_coco(
File "C:\Users\Deltra\anaconda3\lib\site-packages\label_studio_converter\converter.py", line 623, in convert_to_coco
x, y, w, h = self.rotated_rectangle(label)
File "C:\Users\Deltra\anaconda3\lib\site-packages\label_studio_converter\converter.py", line 860, in rotated_rectangle
label["x"],
KeyError: 'x'
```