Grafana hassio add-on won't install

I can not uninstall grafana add-on:

here is error:
18-12-12 17:09:35 INFO (SyncWorker_19) [hassio.docker.interface] Remove Docker hassioaddons/grafana-armhf with latest and None
18-12-12 17:09:35 INFO (MainThread) [hassio.addons.addon] Remove Home Assistant add-on data folder /data/addons/data/a0d7b954_grafana
18-12-12 17:09:35 ERROR (MainThread) [aiohttp.server] Error handling request
Traceback (most recent call last):
File “/usr/local/lib/python3.7/site-packages/aiohttp/web_protocol.py”, line 390, in start
resp = await self._request_handler(request)
File “/usr/local/lib/python3.7/site-packages/aiohttp/web_app.py”, line 366, in _handle
resp = await handler(request)
File “/usr/local/lib/python3.7/site-packages/aiohttp/web_middlewares.py”, line 106, in impl
return await handler(request)
File “/usr/local/lib/python3.7/site-packages/hassio/api/security.py”, line 137, in token_validation
return await handler(request)
File “/usr/local/lib/python3.7/site-packages/hassio/api/utils.py”, line 32, in wrap_api
answer = await method(api, *args, **kwargs)
File “/usr/local/lib/python3.7/site-packages/hassio/addons/utils.py”, line 89, in wrap_check
return await method(addon, *args, **kwargs)
File “/usr/local/lib/python3.7/site-packages/hassio/addons/addon.py”, line 708, in uninstall
await remove_data(self.path_data)
File “/usr/local/lib/python3.7/site-packages/hassio/addons/utils.py”, line 106, in remove_data
if proc.returncode == 0:
UnboundLocalError: local variable ‘proc’ referenced before assignment