AttributeError: 'Lines_LineSeries_LineIterator_DataAccessor_Indicat' object has no attribute '_addobserver'

[utkarsh]

I am facing this error in the following code:
AttributeError: 'Lines_LineSeries_LineIterator_DataAccessor_Indicat' object has no attribute '_addobserver'

import pandas as pd
import yfinance as yf
from datetime import date
import backtrader as bt


cerebro=bt.Cerebro()
data = bt.feeds.PandasData(dataname=yf.download('MSFT', date(2020,1,1), date.today()))
class DonchianChannels(bt.Indicator):
    '''
    Params Note:
      - ``lookback`` (default: -1)
        If `-1`, the bars to consider will start 1 bar in the past and the
        current high/low may break through the channel.
        If `0`, the current prices will be considered for the Donchian
        Channel. This means that the price will **NEVER** break through the
        upper/lower channel bands.
    '''

    alias = ('DCH', 'DonchianChannel',)

    lines = ('dcm', 'dch', 'dcl',)  # dc middle, dc high, dc low
    params = dict(
        period=20,
        lookback=-1,  # consider current bar or not
    )

    plotinfo = dict(subplot=False)  # plot along with data
    plotlines = dict(
        dcm=dict(ls='--'),  # dashed line
        dch=dict(_samecolor=True),  # use same color as prev line (dcm)
        dcl=dict(_samecolor=True),  # use same color as prev line (dch)
    )

    def __init__(self):
        self.dataclose = self.datas[0].close
        hi, lo = self.data.high, self.data.low
        if self.p.lookback:  # move backwards as needed
            hi, lo = hi(self.p.lookback), lo(self.p.lookback)

        self.l.dch = bt.ind.Highest(hi, period=self.p.period)
        self.l.dcl = bt.ind.Lowest(lo, period=self.p.period)
        self.l.dcm = (self.l.dch + self.l.dcl) / 2.0  # avg of the above
    def next(self):
        if self.dataclose[0] > self.l.dch[0]:
            self.sell()
        elif self.dataclose[0] < self.l.dcl[0]:
            self.buy()
cerebro.adddata(data)
cerebro.addstrategy(DonchianChannels)
print('Starting Portfolio Value: %.2f' % cerebro.broker.getvalue())

cerebro.run()
print('Final Portfolio Value: %.2f' % cerebro.broker.getvalue())