Numpy: QLineSeries.appendNp accepts arrays, but doesn't append

from PySide6.QtCore 
import QPointFfrom PySide6.QtWidgets 
import QMainWindow, QApplicationfrom PySide6.QtCharts 
import QChart, QChartView, QLineSeries
import numpy 
import sys

class TestChart(QMainWindow):    
    def __init__(self):        
        super().__init__()        
        self.series = QLineSeries()
        arr1 = numpy.array([2])        
        self.series.appendNp(arr1,arr1)        
        #self.series.append(QPointF(17, 6))        
        print(self.series.count())
        self.chart = QChart()        
        self.chart.addSeries(self.series)    
        self.chart.createDefaultAxes()        
        self._chart_view = QChartView(self.chart)        
        self.setCentralWidget(self._chart_view)

if __name__ == "__main__":    
    app = QApplication(sys.argv)
    window = TestChart()    
    window.show()    
    window.resize(440, 300)    
    sys.exit(app.exec())