ta中技术指标BBI算出来的为NaN？

from tqsdk import TqApi, TqSim
from tqsdk.ta import BBI, ATR

api = TqApi(TqSim())
klines = api.get_kline_serial(“CFFEX.IF1911”, 24 * 60 * 60, data_length=30)
bbi = BBI(klines, 3, 6, 12, 24)
print(list(bbi[“bbi”]))

结果为：

[nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan, nan]