<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def retrieve_diaspora_hcard(handle):
 """ Retrieve a remote Diaspora hCard document. :arg handle: Remote handle to retrieve :return: str (HTML document) """

    webfinger = retrieve_and_parse_diaspora_webfinger(handle)
    document, code, exception = fetch_document(webfinger.get("hcard_url"))
    if exception:
        return None
    return document