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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 _convert_asset_timestamp_fields(dict_):
 """ Takes in a dict of Asset init args and converts dates to pd.Timestamps """

    for key in _asset_timestamp_fields & viewkeys(dict_):
        value = pd.Timestamp(dict_[key], tz='UTC')
        dict_[key] = None if isnull(value) else value
    return dict_