File "/tmp/.mount_electrrnSdPu/usr/lib/python3.7/site-packages/trezorlib/client.py", line 107, in cancel
    self._raw_write(messages.Cancel())
  File "/tmp/.mount_electrrnSdPu/usr/lib/python3.7/site-packages/trezorlib/client.py", line 127, in _raw_write
    self.transport.write(msg_type, msg_bytes)
  File "/tmp/.mount_electrrnSdPu/usr/lib/python3.7/site-packages/trezorlib/transport/protocol.py", line 111, in write
    self.protocol.write(message_type, message_data)
  File "/tmp/.mount_electrrnSdPu/usr/lib/python3.7/site-packages/trezorlib/transport/protocol.py", line 138, in write
    self.handle.write_chunk(chunk)
  File "/tmp/.mount_electrrnSdPu/usr/lib/python3.7/site-packages/trezorlib/transport/webusb.py", line 66, in write_chunk
    assert self.handle is not None