def missing_metadata_field() -> str:
    """Return a schema with missing metadata key."""
    return """{
        "type": "struct",
        "fields": [
            { "type": "string", "nullable": true,
                "name": "name", "metadata": {} },
            { "type": "integer", "nullable": true,
                "name": "empid", "metadata": {} },
            { "type": "boolean", "nullable": true,
                "name": "happy"}
        ]
        }
"""