ValidationError: "String should have at least 1 character" occurs in Copilot Studio Python Client when Activity.text is empty

[runceel]

Overview

When running the sample in Agents-for-python/test_samples/copilot_studio_client_sample, a pydantic_core._pydantic_core.ValidationError is raised if the Activity.text field is an empty string. This causes the application to crash.

Error Details

pydantic_core._pydantic_core.ValidationError: 1 validation error for Activity
text
  String should have at least 1 character [type=string_too_short, input_value='', input_type=str]

Steps to Reproduce

1. Install all required dependencies.
2. Prepare a .env file with valid authentication information.
3. Run the following command in the terminal:

   python app.py
   

4. Start a chat and enter a message.
5. The above error occurs if an empty string is passed to Activity.text.

Expected Behavior

The SDK should gracefully handle cases where Activity.text is empty, and the application should not crash due to a validation error.

Environment

• OS: Windows 11
• Python: 3.13.3
• Copilot Studio Client SDK: 0.0.0a3

Additional Information

• This issue is similar to Agents-for-js #325, where a Zod validation error occurs in the JavaScript SDK for the same reason.
• The .NET SDK does not have this problem.
• In the Python SDK, if Activity.text is empty or missing, a validation error is raised and the application stops.
• Relevant code excerpt from app.py:

  loop.run_until_complete(
      ChatConsoleService(create_mcs_client(mcs_connection_settings)).start_service()
  )

• Please see the attached logs and stack trace for more details.

Traceback (most recent call last):
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\app.py", line 58, in <module>
    loop.run_until_complete(
    ~~~~~~~~~~~~~~~~~~~~~~~^
        ChatConsoleService(create_mcs_client(mcs_connection_settings)).start_service()
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.13_3.13.1008.0_x64__qbz5n2kfra8p0\Lib\asyncio\base_events.py", line 719, in run_until_complete
    return future.result()
           ~~~~~~~~~~~~~^^
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\chat_console_service.py", line 27, in start_service
    async for activity in self._copilot_client.ask_question(question):
        self._print_activity(activity)
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\venv\Lib\site-packages\microsoft\agents\copilotstudio\client\copilot_client.py", line 78, in ask_question
    async for activity in self.ask_question_with_activity(activity):
        yield activity
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\venv\Lib\site-packages\microsoft\agents\copilotstudio\client\copilot_client.py", line 105, in ask_question_with_activity
    async for activity in self.post_request(url, data, headers):
        yield activity
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\venv\Lib\sitio\client\copilot_client.py", line 44, in post_request
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\venv\Lib\site-packages\pydantic\main.py", line 746, in model_validate_json
    return cls.__pydantic_validator__.validate_json(
           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        json_data, strict=strict, context=context, by_alias=by_name
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
pydantic_core._pydantic_core.ValidationError: 1 validation error for Activity
text
  String should have at least 1 character [type=string_too_short, input_value='', input_type=str]
    For further information visit https://errors.pydantic.dev/2.11/v/string_too_short

[sarahcritchley]

Can you retest @runceel and let us know? This should have been fixed recently in an update

[runceel]

Hi @sarahcritchley,

Thanks for the update!

I just tested the latest version of the Copilot Studio Python Client SDK, and unfortunately, the same validation error still occurs when Activity.text is an empty string.

Here is the error message I received:

Traceback (most recent call last):
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.12_3.12.2800.0_x64__qbz5n2kfra8p0\Lib\runpy.py", line 198, in _run_module_as_main
    return _run_code(code, main_globals, None,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.12_3.12.2800.0_x64__qbz5n2kfra8p0\Lib\runpy.py", line 88, in _run_code
    exec(code, run_globals)
  File "c:\Users\kaota\.vscode\extensions\ms-python.debugpy-2025.8.0-win32-arm64\bundled\libs\debugpy\launcher/../..\debugpy\__main__.py", line 71, in <module>
    cli.main()
  File "c:\Users\kaota\.vscode\extensions\ms-python.debugpy-2025.8.0-win32-arm64\bundled\libs\debugpy\launcher/../..\debugpy/..\debugpy\server\cli.py", line 501, in main
    run()
  File "c:\Users\kaota\.vscode\extensions\ms-python.debugpy-2025.8.0-win32-arm64\bundled\libs\debugpy\launcher/../..\debugpy/..\debugpy\server\cli.py", line 351, in run_file
    runpy.run_path(target, run_name="__main__")
  File "c:\Users\kaota\.vscode\extensions\ms-python.debugpy-2025.8.0-win32-arm64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_runpy.py", line 310, in run_path
    return _run_module_code(code, init_globals, run_name, pkg_name=pkg_name, script_name=fname)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "c:\Users\kaota\.vscode\extensions\ms-python.debugpy-2025.8.0-win32-arm64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_runpy.py", line 127, in _run_module_code
    _run_code(code, mod_globals, init_globals, mod_name, mod_spec, pkg_name, script_name)
  File "c:\Users\kaota\.vscode\extensions\ms-python.debugpy-2025.8.0-win32-arm64\bundled\libs\debugpy\_vendored\pydevd\_pydevd_bundle\pydevd_runpy.py", line 118, in _run_code
    exec(code, run_globals)
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\app.py", line 58, in <module>
    loop.run_until_complete(
  File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.12_3.12.2800.0_x64__qbz5n2kfra8p0\Lib\asyncio\base_events.py", line 691, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "D:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\chat_console_service.py", line 27, in start_service
    async for activity in self._copilot_client.ask_question(question):
  File "d:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\.venv\Lib\site-packages\microsoft\agents\copilotstudio\client\copilot_client.py", line 78, in ask_question
    async for activity in self.ask_question_with_activity(activity):
  File "d:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\.venv\Lib\site-packages\microsoft\agents\copilotstudio\client\copilot_client.py", line 105, in ask_question_with_activity
    async for activity in self.post_request(url, data, headers):
  File "d:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\.venv\Lib\site-packages\microsoft\agents\copilotstudio\client\copilot_client.py", line 44, in post_request
    activity = Activity.model_validate_json(activity_data)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "d:\Repos\microsoft\Agents-for-python\test_samples\copilot_studio_client_sample\.venv\Lib\site-packages\pydantic\main.py", line 746, in model_validate_json
    return cls.__pydantic_validator__.validate_json(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
pydantic_core._pydantic_core.ValidationError: 1 validation error for Activity
text
  String should have at least 1 character [type=string_too_short, input_value='', input_type=str]
    For further information visit https://errors.pydantic.dev/2.11/v/string_too_short

Here are the steps I followed:

1. I cloned the repository.
2. In the test_samples folder, I followed the instructions in the README and ran the following commands:

pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-core
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-authorization
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-connector
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-client
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-builder
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-authentication-msal
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-copilotstudio-client
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-hosting-aiohttp
pip install -i https://test.pypi.org/simple/ --extra-index-url https://pypi.org/simple/ microsoft-agents-storage

3. I created a .env file with valid authentication information.
4. I ran python app.py and started a chat.
5. The error occurred when an empty string was passed to Activity.text.

Thanks again for looking into this!

[sarahcritchley]

Thanks @runceel! Triaged and we will explore and provide updates/follow ups cc @axelsrz

[thiborose]

I have the same issue. from my understanding, this happens at

Agents-for-python/libraries/Client/microsoft-agents-copilotstudio-client/microsoft/agents/copilotstudio/client/copilot_client.py

Line 44 in 8258a2b

activity = Activity.model_validate_json(activity_data)

The client attempts to validate all activities based on the Activity Pydantic model, which specifies that text should be a non-empty string:

# microsoft/agents/core/models/activity.py L142
text: NonEmptyString = None

However, some activities that are not of type message have an empty text field. For example, this typing activity creates a validation error because the text field is empty:

{
    "id": "<redacted>",
    "type": "typing",
    "text": "",
    "channelData": {
        "streamType": "streaming",
        "streamId": "<redacted>",
        "chunkType": "delta",
        "streamSequence": 3
    }
}

@sarahcritchley, should the pydantic model be updated so that the Text field is allowed to be empty?

[thiborose]

Well, my local microsoft-agents-core version 0.0.0a3 (which is the latest release) differs from the main branch of the repo.

The latest release has:

# microsoft/agents/core/models/activity.py L142
text: NonEmptyString = None

The main branch here has:

Agents-for-python/libraries/Core/microsoft-agents-core/microsoft/agents/core/models/activity.py

Line 142 in 8258a2b

text: str = None

So I guess this is already resolved and it's just about making a new release?

EDIT: Indeed this has been fixed: f2bd502

[thiborose]

As a temporary workaround, I setup my project like that:

# Install all dependencies except microsoft-agents-core and microsoft-agents-copilotstudio-client
uv sync

# then, install separately, from source, in this exact order:
uv pip install "git+https://github.com/microsoft/Agents-for-python.git@8258a2b691e94b2bd053cec806d1abd9e1457b86#subdirectory=libraries/Core/microsoft-agents-core"

uv pip install "git+https://github.com/microsoft/Agents-for-python.git@8258a2b691e94b2bd053cec806d1abd9e1457b86#subdirectory=libraries/Client/microsoft-agents-copilotstudio-client"

This will install the package from the Github repo directly as of today's commit

[axelsrz]

@sarahcritchley @thiborose this was resolved in #52 the fix will come with the next release or if you pull from current main