fix: resolve AttributeError by supporting both Pydantic and Protobuf AgentCard serialization

PiperOrigin-RevId: 918921714

Author: vertex-sdk-bot

agentplatform/_genai/_agent_engines_utils.py

@@ -652,8 +652,8 @@ def _generate_class_methods_spec_or_raise(
 
             class_method = _to_proto(schema_dict)
             class_method[_MODE_KEY_IN_SCHEMA] = mode
-            if hasattr(agent, "agent_card"):
-                class_method[_A2A_AGENT_CARD] = json_format.MessageToJson(
+            if hasattr(agent, "agent_card") and getattr(agent, "agent_card") is not None:
+                class_method[_A2A_AGENT_CARD] = _serialize_agent_card_to_json(
                     getattr(agent, "agent_card")
                 )
             class_methods_spec.append(class_method)
@@ -2263,3 +2263,57 @@ def _import_autogen_tools_or_warn() -> Optional[types.ModuleType]:
             "call `pip install google-cloud-aiplatform[ag2]`."
         )
     return None
+
+
+def _serialize_agent_card_to_dict(card: Any) -> Optional[Dict[str, Any]]:
+    """Validates and serializes an AgentCard to a dictionary representation.
+
+    Args:
+        card: The AgentCard instance (must be a Protobuf Message).
+
+    Returns:
+        The serialized card as a dictionary.
+
+    Raises:
+        TypeError: If the card type is not a Protobuf Message (e.g., Pydantic).
+    """
+    if card is None:
+        return None
+
+    if hasattr(card, "DESCRIPTOR"):
+        from google.protobuf import json_format
+
+        return typing.cast(dict[str, Any], json_format.MessageToDict(card))
+
+    raise TypeError(
+        f"Unsupported AgentCard type: {type(card)}. "
+        "The agentplatform namespace exclusively supports Protobuf Messages. "
+        "Pydantic models are not supported."
+    )
+
+
+def _serialize_agent_card_to_json(card: Any) -> Optional[str]:
+    """Validates and serializes an AgentCard to a JSON string representation.
+
+    Args:
+        card: The AgentCard instance (must be a Protobuf Message).
+
+    Returns:
+        The serialized card as a JSON string.
+
+    Raises:
+        TypeError: If the card type is not a Protobuf Message (e.g., Pydantic).
+    """
+    if card is None:
+        return None
+
+    if hasattr(card, "DESCRIPTOR"):
+        from google.protobuf import json_format
+
+        return typing.cast(str, json_format.MessageToJson(card))
+
+    raise TypeError(
+        f"Unsupported AgentCard type: {type(card)}. "
+        "The agentplatform namespace exclusively supports Protobuf Messages. "
+        "Pydantic models are not supported."
+    )

agentplatform/_genai/agent_engines.py

@@ -2498,12 +2498,12 @@ def _create_config(
 
             if hasattr(agent, "agent_card"):
                 agent_card = getattr(agent, "agent_card")
-                if agent_card:
+                if agent_card is not None:
                     try:
-                        from google.protobuf import json_format
-
-                        agent_engine_spec["agent_card"] = json_format.MessageToDict(
-                            agent_card
+                        agent_engine_spec["agent_card"] = (
+                            _agent_engines_utils._serialize_agent_card_to_dict(
+                                agent_card
+                            )
                         )
                     except Exception as e:
                         raise ValueError(

agentplatform/agent_engines/_agent_engines.py

@@ -2005,11 +2005,11 @@ def _generate_class_methods_spec_or_raise(
             class_method[_MODE_KEY_IN_SCHEMA] = mode
             # A2A agent card is a special case, when running in A2A mode,
             if hasattr(agent_engine, "agent_card"):
-                from google.protobuf import json_format
-
-                class_method[_A2A_AGENT_CARD] = json_format.MessageToJson(
-                    getattr(agent_engine, "agent_card")
-                )
+                card = getattr(agent_engine, "agent_card")
+                if card is not None:
+                    class_method[_A2A_AGENT_CARD] = (
+                        _agent_engines_utils._serialize_agent_card_to_json(card)
+                    )
             class_methods_spec.append(class_method)
 
     return class_methods_spec