打开cta回测页面就弹出错误提示，小白求助，请问这是什么原因引起的，如何修复？谢谢
Traceback (most recent call last):
File "D:\software\Anaconda3\lib\site-packages\vnpy\trader\ui\mainwindow.py", line 281, in open_widget
widget = widget_class(self.main_engine, self.event_engine)
File "D:\software\Anaconda3\lib\site-packages\vnpy\app\cta_backtester\ui\widget.py", line 48, in init
self.init_ui()
File "D:\software\Anaconda3\lib\site-packages\vnpy\app\cta_backtester\ui\widget.py", line 210, in init_ui
self.candle_dialog = CandleChartDialog()
File "D:\software\Anaconda3\lib\site-packages\vnpy\app\cta_backtester\ui\widget.py", line 1142, in init
self.init_ui()
File "D:\software\Anaconda3\lib\site-packages\vnpy\app\cta_backtester\ui\widget.py", line 1152, in init_ui
self.chart.add_plot("volume", maximum_height=200)
File "D:\software\Anaconda3\lib\site-packages\vnpy\chart\widget.py", line 72, in add_plot
plot = pg.PlotItem(axisItems={'bottom': self._x_axis})
File "D:\software\Anaconda3\lib\site-packages\pyqtgraph\graphicsItems\PlotItem\PlotItem.py", line 158, in init
self.setAxisItems(axisItems)
File "D:\software\Anaconda3\lib\site-packages\pyqtgraph\graphicsItems\PlotItem\PlotItem.py", line 325, in setAxisItems
if axis != self.axes[k]["item"]:
KeyError: 'bottom'
