def METHOD_NAME(connections: List[Connection] = []) -> List[Mapping[str, Optional[str]]]:
    serialized_connections = []
    for c in connections:
        serialized_connection = {
            "conn_id": c.conn_id,
            "conn_type": c.conn_type,
        }
        if hasattr(c, "login") and c.login:
            serialized_connection["login"] = c.login
        if hasattr(c, "password") and c.password:
            serialized_connection["password"] = c.password
        if hasattr(c, "host") and c.host:
            serialized_connection["host"] = c.host
        if hasattr(c, "schema") and c.schema:
            serialized_connection["schema"] = c.schema
        if hasattr(c, "port") and c.port:
            serialized_connection["port"] = c.port
        if hasattr(c, "extra") and c.extra:
            serialized_connection["extra"] = c.extra
        if hasattr(c, "description") and c.description:
            serialized_connection["description"] = c.description
        serialized_connections.append(serialized_connection)
    return serialized_connections