Fix/Process content if the structuredContent are null

[msureshkumar88]

Fix OutputLengthGuard plugin null structuredContent handling

🔗 Related Issue

Closes #4248

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📝 Summary

Fixed a bug in the OutputLengthGuard plugin where tool output was not being truncated when structuredContent was explicitly set to null. The plugin was checking for key presence but not validating the value, causing it to enter the structured content processing branch with a null value and skip content array processing entirely.

Changes:

• Added null check to structuredContent key validation in output_length_guard.py (lines 249-254)
• Added regression test test_null_structured_content_processes_content_array() to verify the fix

Impact:

• Tools returning structuredContent: null now correctly have their content array truncated
• Fixes the exact scenario reported in issue [BUG]: Output Length Guard Plugin not limiting different structs #4248 (63 chars → 10 chars truncation)

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🏷️ Type of Change

• Bug fix
• Feature / Enhancement
• Documentation
• Refactor
• Chore (deps, CI, tooling)
• Other (describe below)

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🧪 Verification

Check	Command	Status
Lint suite	make lint	✅
Unit tests	make test	✅ 315 passed, 1 skipped in 0.74s
Coverage ≥ 80%	make coverage	✅

Test Coverage:

• New test added: test_null_structured_content_processes_content_array()
• All existing tests continue to pass
• Verifies exact scenario from issue [BUG]: Output Length Guard Plugin not limiting different structs #4248

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✅ Checklist

• Code formatted (make black isort pre-commit)
• Tests added/updated for changes
• Documentation updated (if applicable)
• No secrets or credentials committed
• DCO sign-off included in commits

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📓 Notes

Root Cause

The plugin's logic checked for the presence of the structuredContent key but didn't validate whether the value was null:

# Before (buggy):
if "structuredContent" in result:
    struct_key = "structuredContent"

# After (fixed):
if "structuredContent" in result and result["structuredContent"] is not None:
    struct_key = "structuredContent"

When tools returned {"structuredContent": null, "content": [...]}, the plugin would:

1. Detect the structuredContent key exists
2. Enter the structured content processing branch
3. Fail to process the null value
4. Skip content array processing entirely

Testing

The new test verifies the exact scenario from issue #4248:

• Tool returns structuredContent: null with a 63-character content array
• Plugin configured with max_output_length: 10
• Expected: Content truncated to 10 characters
• Result: ✅ Content correctly truncated

Next Steps for Verification

1. Restart the gateway to load the fixed plugin code
2. Test with the echo tool - output should now truncate to 10 characters
3. Verify in logs: "Plugin OutputLengthGuardPlugin executed successfully"

[madhu-mohan-jaishankar]

LGTM.

[ja8zyjits]

LGTM