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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def QueryFields(r, what, fields=None):
 """ Retrieves available fields for a resource. @type what: string @param what: Resource name, one of L{constants.QR_VIA_RAPI} @type fields: list of string @param fields: Requested fields @rtype: string @return: job id """


    query = {}

    if fields is not None:
        query["fields"] = ",".join(fields)

    return r.request("get", "/2/query/%s/fields" % what, query=query)