def METHOD_NAME(logger: logging.Logger, source: Optional["Source"]) -> str:
    """
    Creates a message indicating where to look in the documentation for
    more information on a given source by checking the spec of that source
    (if provided) for a 'documentationUrl'.
    :param logger: source logger
    :param source: optional (source)
    :return: A message telling the user where to go to learn more about the source.
    """
    if not source:
        return "Please visit the connector's documentation to learn more. "
    try:
        connector_spec = source.spec(logger)
        docs_url = connector_spec.documentationUrl
        if docs_url:
            return f"Please visit {docs_url} to learn more. "
        else:
            return "Please visit the connector's documentation to learn more. "
    except FileNotFoundError:  # If we are unit testing without implementing spec() method in source
        if source:
            docs_url = f"https://docs.airbyte.com/integrations/sources/{source.name}"
        else:
            docs_url = "https://docs.airbyte.com/integrations/sources/test"
        return f"Please visit {docs_url} to learn more."