Registered new object after initialization error using pyqtlet

I'm discovering Leaflet (especially the equivalent in Python pyqlet), and there is something I do not understand. I adapted this code from the documentation so when I type the Space bar, the marker present on the map is changed (here I just change the text of the popup)

import sys
from PyQt5.QtWidgets import QApplication, QVBoxLayout, QWidget
from PyQt5.Qt import Qt
from pyqtlet import L, MapWidget
from time import time

class MapWindow(QWidget):
    def __init__(self):
        # Setting up the widgets and layout
        super().__init__()
        self.mapWidget = MapWidget()
        self.layout = QVBoxLayout()
        self.layout.addWidget(self.mapWidget)
        self.setLayout(self.layout)

        # Working with the maps with pyqtlet
        self.map = L.map(self.mapWidget)
        self.map.setView([12.97, 77.59], 10)
        L.tileLayer('https://{s}.basemaps.cartocdn.com/rastertiles/voyager_nolabels/{z}/{x}/{y}{r}.png').addTo(self.map)
        self.marker = L.marker([12.934056, 77.610029])
        self.marker.bindPopup('Maps are a treasure.')
        self.map.addLayer(self.marker)
        self.show()
    
    def keyPressEvent(self, event):
        if event.key() == Qt.Key_Space:
            self.newMarker()

    def newMarker(self):
        self.map.removeLayer(self.marker)
        self.marker = L.marker([12.934056, 77.610029])
        self.marker.bindPopup(str(time()))      # put the current time as message
        self.map.addLayer(self.marker)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    widget = MapWindow()
    sys.exit(app.exec_())

On the execution, when I use the space bar, the marker is indeed changed but some messages appear in the console (and my research on the web have not been helpful) :

js: Uncaught TypeError: Cannot read property 'mapObject' of null
<*>Registered new object after initialization, existing clients won't be notified!
<*>Registered new object after initialization, existing clients won't be notified!
js: Unhandled signal: l2Object::0
<*>Registered new object after initialization, existing clients won't be notified!
js: Unhandled signal: l3Object::0

The symbol <*> corresponds to when I type the key, it doesn't appear in the terminal.

The first line always appears, but as it is also the case on the code from the documentation, I guess this is not critical.

Is there something I did the wrong way somewhere ?