sage notebook() errors

sage   
┌────────────────────────────────────────────────────────────────────┐
│ SageMath version 8.6, Release Date: 2019-01-15                     │
│ Using Python 2.7.16. Type "help()" for help.                       │
└────────────────────────────────────────────────────────────────────┘
sage: 
sage: notebook()
('The notebook files are stored in:', 'sage_notebook.sagenb')
┌────────────────────────────────────────────────┐
│                                                │
│ Open your web browser to http://localhost:8080 │
│                                                │
└────────────────────────────────────────────────┘
Executing twistd  --pidfile="sage_notebook.sagenb/sagenb.pid" -ny "sage_notebook.sagenb/twistedconf.tac"
2019-06-05T22:57:51+0900 [-] Loading sage_notebook.sagenb/twistedconf.tac...
2019-06-05T22:57:52+0900 [-] Loaded.
2019-06-05T22:57:52+0900 [twisted.scripts._twistd_unix.UnixAppLogger#info] twistd 18.9.0 (/nix/store/snprfi0acg5bpbzhrggri7q85wvf0v0g-python-2.7.16/bin/python2.7 2.7.16) starting up.
2019-06-05T22:57:52+0900 [twisted.scripts._twistd_unix.UnixAppLogger#info] reactor class: twisted.internet.epollreactor.EPollReactor.
2019-06-05T22:57:52+0900 [-] QuietSite starting on 8080
2019-06-05T22:57:52+0900 [__builtin__.QuietSite#info] Starting factory <__builtin__.QuietSite instance at 0x7f47a4a3f7a0>
Fontconfig warning: "/etc/fonts/fonts.conf", line 86: unknown element "blank"
404 Not Found: The requested URL was not found on the server.  If you entered the URL manually please check your spelling and try again.
Traceback (most recent call last):
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/sagenb/flask_version/base.py", line 75, in static_view_func
    return send_from_directory(root_path, filename)
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/flask/helpers.py", line 709, in send_from_directory
    raise NotFound()
NotFound: 404 Not Found: The requested URL was not found on the server.  If you entered the URL manually please check your spelling and try again.
404 Not Found: The requested URL was not found on the server.  If you entered the URL manually please check your spelling and try again.
Traceback (most recent call last):
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/sagenb/flask_version/base.py", line 75, in static_view_func
    return send_from_directory(root_path, filename)
  File "/nix/store/sz5k2ml5gfvxf3dasrxibyszw8ad4m7n-python-2.7.16-env/lib/python2.7/site-packages/flask/helpers.py", line 709, in send_from_directory
    raise NotFound()
NotFound: 404 Not Found: The requested URL was not found on the server.  If you entered the URL manually please check your spelling and try again.