KeyError: 'annotation' in fit() when handling /webhook events without annotation payload

[xiaoyao9184]

When receiving a /webhook POST from Label Studio, the ML backend crashes with a KeyError: 'annotation' in examples/bert_classifier/model.py, specifically inside the fit() method:

[2025-05-14 10:33:06,753] [WARNING] [werkzeug::_log::97]  * Debugger is active!
[2025-05-14 10:33:06,754] [INFO] [werkzeug::_log::97]  * Debugger PIN: 485-577-215
[2025-05-14 10:33:18,338] [INFO] [werkzeug::_log::97] 172.16.22.2 - - [14/May/2025 10:33:18] "POST /webhook HTTP/1.1" 500 -
Traceback (most recent call last):
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/flask/app.py", line 2213, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/flask/app.py", line 2193, in wsgi_app
    response = self.handle_exception(e)
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/flask/app.py", line 2190, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/flask/app.py", line 1486, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/flask/app.py", line 1484, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/flask/app.py", line 1469, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
  File "/home/ubuntu/.conda/envs/label-studio/lib/python3.10/site-packages/label_studio_ml/api.py", line 126, in webhook
    result = model.fit(event, data)
  File "/home/ubuntu/code/label-studio-ml-backend/label_studio_ml/examples/bert_classifier/model.py", line 125, in fit
    project_id = data['annotation']['project']
KeyError: 'annotation'

Looking at this line

label-studio-ml-backend/label_studio_ml/examples/bert_classifier/model.py

Line 125 in 2ba5455

project_id = data['annotation']['project']

However, according to the surrounding code, project_id has already been provided as a constructor argument to the model.

label-studio-ml-backend/label_studio_ml/api.py

Lines 117 to 125 in 2ba5455

	@_server.route('/webhook', methods=['POST'])
	def webhook():
	data = request.json
	event = data.pop('action')
	if event not in TRAIN_EVENTS:
	return jsonify({'status': 'Unknown event'}), 200
	project_id = str(data['project']['id'])
	label_config = data['project']['label_config']
	model = MODEL_CLASS(project_id, label_config=label_config)

)

I've forked the repository and updated the following example models to use self.project_id instead:

• bert_classifier
• huggingface_ner
• sklearn_text_classifier

However, I have not yet run the full test suite or studied the full contribution guidelines, as I’m not deeply familiar with this codebase yet.

Would it be acceptable to open a PR with this minimal fix and receive further guidance from maintainers? Or would you prefer I do more in-depth validation first?

[makseq]

Are you sure "Send payload" toggle is on in the Webhook settings?

[xiaoyao9184]

Yes, I'm using the docker:latest image, which corresponds to version 1.17.0.
I haven't verified yet whether the same issue exists in later versions.

docker inspect heartexlabs/label-studio:latest
[
    {
        "Id": "sha256:cc46d8f13b2378cc089ad1f3424788e883fc1a651fc45892e76c01802c0f9a9e",
        "RepoTags": [
            "heartexlabs/label-studio:latest"
        ],
        "RepoDigests": [
            "heartexlabs/label-studio@sha256:9e537980c551ced53188844e3708e470c8086e2cc578a36b4cbc2a2b9a2caae4"
        ],

[ginic]

I have put up a pull request that I believe should fix this at #790