Traceback (most recent call last):
  File "...\wslink\websocket.py", line 275, in onMessage
    results = func(obj, *args, **kwargs)
  File "...\vtk\web\protocols.py", line 379, in addRenderObserver
    self.publish('viewport.image.push.subscription', pushRender())
  File "...\vtk\web\protocols.py", line 337, in pushRender
    reply = self.stillRender({ "view": realViewId, "mtime": self.trackingViews[vId]["mtime"] })
  File "...\vtk\web\protocols.py", line 309, in stillRender
    reply["memsize"] = reply_image.GetDataSize() if reply_image else 0
AttributeError: 'str' object has no attribute 'GetDataSize'