fix: resolve AttributeError when serializing agent instances with diverse card format architectures

PiperOrigin-RevId: 927226105

Author: vertex-sdk-bot

vertexai/_genai/_agent_engines_utils.py

@@ -653,9 +653,9 @@ 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(
-                    getattr(agent, "agent_card")
-                )
+                card = getattr(agent, "agent_card")
+                if card is not None:
+                    class_method[_A2A_AGENT_CARD] = _serialize_agent_card_to_json(card)
             class_methods_spec.append(class_method)
 
     return class_methods_spec
@@ -2148,3 +2148,59 @@ def _add_telemetry_enablement_env(
         return env_vars
 
     return env_vars | env_to_add
+
+
+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 (Pydantic model or Protobuf Message).
+
+    Returns:
+        The serialized card as a dictionary.
+
+    Raises:
+        TypeError: If the card type is not supported.
+    """
+    if card is None:
+        return None
+
+    if hasattr(card, "model_dump"):
+        return typing.cast(dict[str, Any], card.model_dump(exclude_none=True))
+    elif hasattr(card, "DESCRIPTOR"):
+        from google.protobuf import json_format
+
+        return typing.cast(dict[str, Any], json_format.MessageToDict(card))
+    else:
+        raise TypeError(
+            f"Unsupported AgentCard type: {type(card)}. "
+            "Only Pydantic models and Protobuf Messages are 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 (Pydantic model or Protobuf Message).
+
+    Returns:
+        The serialized card as a JSON string.
+
+    Raises:
+        TypeError: If the card type is not supported.
+    """
+    if card is None:
+        return None
+
+    if hasattr(card, "model_dump_json"):
+        return typing.cast(str, card.model_dump_json())
+    elif hasattr(card, "DESCRIPTOR"):
+        from google.protobuf import json_format
+
+        return typing.cast(str, json_format.MessageToJson(card))
+    else:
+        raise TypeError(
+            f"Unsupported AgentCard type: {type(card)}. "
+            "Only Pydantic models and Protobuf Messages are supported."
+        )

vertexai/_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(

vertexai/agent_engines/_agent_engines.py

@@ -1997,11 +1997,11 @@ 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] = (
+                        _utils._serialize_agent_card_to_json(card)
+                    )
             class_methods_spec.append(class_method)
 
     return class_methods_spec