ReqIF: Import/export of TAG fields

[mettta]

INFO:     127.0.0.1:53295 - "GET /reqif/export_tree HTTP/1.1" 500 Internal Server Error
ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/uvicorn/protocols/http/httptools_impl.py", line 419, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/uvicorn/middleware/proxy_headers.py", line 78, in __call__
    return await self.app(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/fastapi/applications.py", line 271, in __call__
    await super().__call__(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/applications.py", line 118, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/middleware/cors.py", line 84, in __call__
    await self.app(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/fastapi/middleware/asyncexitstack.py", line 21, in __call__
    raise e
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/fastapi/middleware/asyncexitstack.py", line 18, in __call__
    await self.app(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/routing.py", line 706, in __call__
    await route.handle(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/routing.py", line 66, in app
    response = await func(request)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/fastapi/routing.py", line 237, in app
    raw_response = await run_endpoint_function(
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/fastapi/routing.py", line 165, in run_endpoint_function
    return await run_in_threadpool(dependant.call, **values)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/starlette/concurrency.py", line 41, in run_in_threadpool
    return await anyio.to_thread.run_sync(func, *args)
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/anyio/to_thread.py", line 31, in run_sync
    return await get_asynclib().run_sync_in_worker_thread(
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/anyio/_backends/_asyncio.py", line 937, in run_sync_in_worker_thread
    return await future
  File "/Users/mettta/Projects/dev/strictdoc/.venv-default/lib/python3.9/site-packages/anyio/_backends/_asyncio.py", line 867, in run
    result = context.run(func, *args)
  File "/Users/mettta/Projects/dev/strictdoc/./strictdoc/server/routers/main_router.py", line 1994, in get_reqif_export_tree
    reqif_bundle = SDocToReqIFObjectConverter.convert_document_tree(
  File "/Users/mettta/Projects/dev/strictdoc/./strictdoc/backend/reqif/export/sdoc_to_reqif_converter.py", line 186, in convert_document_tree
    raise NotImplementedError(field) from None
NotImplementedError: GrammarElementFieldTag(title = "UNIT", required = True, _tx_position = 336, _tx_position_end = 385, parent = GrammarElement(...), gef_type = "Tag")
INFO:     connection closed