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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 get_hgnc_name(hgnc_id):
 """Return the HGNC symbol corresponding to the given HGNC ID. Parameters hgnc_id : str The HGNC ID to be converted. Returns ------- hgnc_name : str The HGNC symbol corresponding to the given HGNC ID. """

    try:
        hgnc_name = hgnc_names[hgnc_id]
    except KeyError:
        xml_tree = get_hgnc_entry(hgnc_id)
        if xml_tree is None:
            return None
        hgnc_name_tag =\
            xml_tree.find("result/doc/str[@name='symbol']")
        if hgnc_name_tag is None:
            return None
        hgnc_name = hgnc_name_tag.text.strip()
    return hgnc_name