python用QChart画折线图时Y轴无数据如何显示为空？

Question

如下，当X轴大于20时，Y轴为数据为空，如何在图上显示出来？
但不能显示为0

import sys
from PyQt5.QtGui import QPainter
from PyQt5.QtWidgets import QApplication, QMainWindow
from  PyQt5.QtChart import QChart, QChartView, QLineSeries
 
class DemoChartLineSeries(QMainWindow):
    def __init__(self, parent=None):
        super(DemoChartLineSeries, self).__init__(parent)   
        
         # 设置窗口标题
        self.setWindowTitle('QChart折线图演示')      
        # 设置窗口大小
        self.resize(480, 360)
        
        self.createChart()
    
    def createChart(self):
            
        #设置折线数据
        lineSeries = QLineSeries()
        lineSeries.append(0, 6)
        lineSeries.append(2, 4)
        lineSeries.append(3, 8)
        lineSeries.append(7, 4)
        lineSeries.append(10, 5)
        lineSeries.append(11, 1)
        lineSeries.append(13, 3)
        lineSeries.append(17, 6)
        lineSeries.append(18, 3)
        lineSeries.append(20, 2)
        # lineSeries.append(21, None)
        # lineSeries.append(22, None)
        # lineSeries.append(23, None)

        
        #创建图表
        chart = QChart()
        chart.legend().hide()
        chart.addSeries(lineSeries)
        chart.createDefaultAxes()
        chart.setTitle('一个简单的折线图示例')
        
        #图表视图
        chartView = QChartView(chart)
        chartView.setRenderHint(QPainter.Antialiasing)
        
        self.setCentralWidget(chartView)
      
        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = DemoChartLineSeries()
    window.show()
    sys.exit(app.exec())   

Answer 1

判断下，如果没有数据，就将那个点设置为空白