After a while without matching results, I got this error.

`Exception raised when trying to compute indicators on BTCUPUSDT
Error: data_len < period
Traceback (most recent call last):
File "/usr/local/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 2646, in get_loc
return self._engine.get_loc(key)
File "pandas/_libs/index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 1619, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 1627, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'low_boll'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "TradingModel.py", line 149, in
Main()
File "TradingModel.py", line 141, in Main
if model.bollStrategy(len(model.df['close'])-1):
File "TradingModel.py", line 119, in bollStrategy
buy_price = 0.98 * df['low_boll'][i]
File "/usr/local/lib/python3.7/site-packages/pandas/core/frame.py", line 2800, in getitem
indexer = self.columns.get_loc(key)
File "/usr/local/lib/python3.7/site-packages/pandas/core/indexes/base.py", line 2648, in get_loc
return self._engine.get_loc(self._maybe_cast_indexer(key))
File "pandas/_libs/index.pyx", line 111, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/index.pyx", line 138, in pandas._libs.index.IndexEngine.get_loc
File "pandas/_libs/hashtable_class_helper.pxi", line 1619, in pandas._libs.hashtable.PyObjectHashTable.get_item
File "pandas/_libs/hashtable_class_helper.pxi", line 1627, in pandas._libs.hashtable.PyObjectHashTable.get_item
KeyError: 'low_boll'`