'Get the latest minute on or before ``dt`` in which ``asset`` traded.
If there are no trades on or before ``dt``, returns ``pd.NaT``.
Parameters
asset : zipline.asset.Asset
The asset for which to get the last traded minute.
dt : pd.Timestamp
The minute at which to start searching for the last traded minute.
Returns
last_traded : pd.Timestamp
The dt of the last trade for the given asset, using the input
dt as a vantage point.'

def get_last_traded_dt(self, asset, dt):

    rf = self._roll_finders[asset.roll_style]
    sid = rf.get_contract_center(asset.root_symbol, dt, asset.offset)
    if (sid is None):
        return pd.NaT
    contract = rf.asset_finder.retrieve_asset(sid)
    return self._bar_reader.get_last_traded_dt(contract, dt)
