Python: Fixed empty text content pydantic validation failure

[howlowck]

Motivation and Context

Currently when using the Python AzureAIClient, the streaming response will emit empty text deltas. When using it in conjunction with AG-UI, it results in a pydantic validation error.

.../site-packages/pydantic/main.py", line 250, in __init__
    validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
pydantic_core._pydantic_core.ValidationError: 1 validation error for TextMessageContentEvent
delta
  String should have at least 1 character [type=string_too_short, input_value='', input_type=str]
    For further information visit https://errors.pydantic.dev/2.12/v/string_too_short

Description

Added a simple empty-string check, and if it's empty, skip adding the events to be emitted.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• This is not a breaking change

Screenshots

Added "empty string" test case passes

cc. @lordlinus

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/ag-ui/agent_framework_ag_ui
_events.py	324	18	94%	223, 244, 273, 290, 313, 326, 358, 367–370, 431–432, 436, 497–498, 577, 590
TOTAL	15889	2416	84%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2283	130 💤	0 ❌	0 🔥	57.443s ⏱️

[Copilot]

Pull request overview

This PR fixes a Pydantic validation error that occurs when empty text deltas are emitted during streaming responses in the Python AzureAIClient. The AG-UI library validates that text message content events must have non-empty strings, so empty chunks need to be filtered out.

Key Changes:

• Added validation to skip empty text content chunks before emitting events
• Added test coverage for the empty text chunk scenario

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
python/packages/ag-ui/agent_framework_ag_ui/_events.py	Added empty string check in _handle_text_content to skip emitting events for empty text chunks
python/packages/ag-ui/tests/test_events_comprehensive.py	Added test_empty_text_message_streaming to verify empty chunks are properly skipped while maintaining message continuity