microsoft/autogen · error · UnsupportedKeywordError

Unsupported or missing type `{json_type}` in union

Error message

Unsupported or missing type `{json_type}` in union

What it means

Error "Unsupported or missing type `{json_type}` in union" thrown in microsoft/autogen.

Source

Thrown at python/packages/autogen-core/src/autogen_core/utils/_json_to_pydantic.py:187

            for k, v in schema.items():
                if k not in {"allOf", "properties", "required"}:
                    merged[k] = v
            merged["required"] = list(set(merged["required"]))
            schema = merged

        return self._json_schema_to_model(schema, model_name, root_schema)

    def _resolve_union_types(self, schemas: List[Dict[str, Any]]) -> List[Any]:
        types: List[Any] = []
        for s in schemas:
            if "$ref" in s:
                types.append(self.get_ref(s["$ref"].split("/")[-1]))
            elif "enum" in s:
                types.append(Literal[tuple(s["enum"])] if len(s["enum"]) > 0 else Any)
            else:
                json_type = s.get("type")
                if json_type not in TYPE_MAPPING:
                    raise UnsupportedKeywordError(f"Unsupported or missing type `{json_type}` in union")

                # Handle array types with items specification
                if json_type == "array" and "items" in s:
                    item_schema = s["items"]
                    if "$ref" in item_schema:
                        item_type = self.get_ref(item_schema["$ref"].split("/")[-1])
                    else:
                        item_type_name = item_schema.get("type")
                        if item_type_name is None:
                            item_type = str
                        elif item_type_name not in TYPE_MAPPING:
                            raise UnsupportedKeywordError(f"Unsupported item type `{item_type_name}` in union array")
                        else:
                            item_type = TYPE_MAPPING[item_type_name]

                    constraints = {}
                    if "minItems" in s:
                        constraints["min_length"] = s["minItems"]

View on GitHub (pinned to 027ecf0a37)

Solutions

1. Use only supported JSON types inside unions

Example fix

Replace the unsupported union member with a supported type

When it happens

Trigger: Thrown at python/packages/autogen-core/src/autogen_core/utils/_json_to_pydantic.py:187 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/autogen@027ecf0a37 (2026-08-15). Data as JSON: /api/errors/b6db1f52d5ddd6bd. Report an issue: GitHub.