Yup, the error message is known and occurs when a specific situation is reached.
This is the code that causes it
The get_keys() method uses the trucated api key text from the button to get the full keys from the api_keys.json file. If either public or secret key are ‘None’ then it fails and shows the error you can see.
Could you check in your api_keys.json file and see if the keys are set properly there?
They should be in the format [{"exchange": "ccedk", "public": "public_key", "secret": "secret_key"}]
Edit: Just saw your reply about the keys existing in api_keys.json
Have you restarted Plunge since adding the keys?