fix: AdCP responses now properly omit null/empty optional fields

[bokelley]

Problem

The AdCP JSON schema does not allow null values for optional fields. According to the spec, optional fields should be omitted entirely, not set to null or empty values.

Issues:

1. ListAuthorizedPropertiesResponse was explicitly setting errors=[], causing it to be included in responses
2. AdCPBaseModel.model_dump() wasn't using exclude_none=True by default
3. Tests were incorrectly validating that ALL optional fields must be present

Example of incorrect behavior:

{
  "publisher_domains": ["example.com"],
  "errors": [],           // ❌ Should be omitted
  "primary_channels": null // ❌ Should be omitted
}

Correct behavior:

{
  "publisher_domains": ["example.com"]
  // ✅ Optional fields omitted
}

Root Causes

1. Missing exclude_none in AdCPBaseModel.model_dump()

AdCPBaseModel didn't set exclude_none=True by default, so None-valued fields were included in serialization.

2. Incorrect override in ListAuthorizedPropertiesResponse.model_dump()

Lines 3444-3446 in schemas.py were converting errors=None to errors=[]:

def model_dump(self, **kwargs) -> dict[str, Any]:
    data = super().model_dump(**kwargs)
    if data.get("errors") is None:
        data["errors"] = []  # ❌ Violates AdCP spec
    return data

3. Explicit errors=[] in tool code

src/core/tools/properties.py line 202 was setting errors=[] explicitly, causing it to be included even though it had no errors.

Solution

1. Added model_dump() to AdCPBaseModel

def model_dump(self, **kwargs):
    """Dump model with AdCP-compliant defaults."""
    if "exclude_none" not in kwargs:
        kwargs["exclude_none"] = True
    return super().model_dump(**kwargs)

Now all AdCP response models automatically omit None-valued optional fields.

2. Fixed ListAuthorizedPropertiesResponse.model_dump()

Removed the override that was converting None to []. Now delegates to parent:

def model_dump(self, **kwargs) -> dict[str, Any]:
    """Return AdCP-compliant response."""
    return super().model_dump(**kwargs)

3. Removed explicit errors=[] from tool code

Properties tool no longer sets errors=[] when there are no errors.

Testing

✅ 48/48 AdCP contract tests passing
✅ 829/829 unit tests passing
✅ Updated 4 unit tests to verify omission behavior
✅ Updated 1 integration test to verify MCP/A2A parity with new behavior

Tests now verify:

• Required fields are always present
• Optional fields with None values are omitted
• Optional fields with actual values are included
• Both MCP and A2A return identical response data

Impact

Breaking Change: ⚠️ Clients expecting all optional fields to be present (even with null/empty values) will need to handle omitted fields.

Benefits:

• ✅ Full compliance with AdCP JSON schema spec
• ✅ Prevents validation errors from strict AdCP consumers
• ✅ Reduces payload size (no unnecessary null/empty fields)
• ✅ More idiomatic JSON (optional fields are truly optional)

Scope:

• Affects all AdCP response models that inherit from AdCPBaseModel
• Most visible in ListAuthorizedPropertiesResponse responses
• No changes to request handling or validation

Files Changed

1. src/core/schemas.py (2 changes)

   • Added model_dump() override to AdCPBaseModel with exclude_none=True
   • Fixed ListAuthorizedPropertiesResponse.model_dump() to delegate to parent

2. src/core/tools/properties.py (1 change)

   • Removed explicit errors=[] assignment

3. tests/unit/test_adcp_contract.py (4 test updates)

   • Updated assertions to verify omission instead of presence

4. tests/unit/test_authorized_properties.py (2 test updates)

   • Updated to verify AdCP-compliant omission behavior

5. tests/integration/test_a2a_response_compliance.py (1 test update)

   • Updated MCP/A2A parity test to expect omitted fields

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com