TypeError: Consumer key must be string or bytes, not NoneType when authentication

Question

Planning to use variables to authorize tweepy with Twitter's API, but it shows the following:
TypeError: Consumer key must be string or bytes, not NoneType when authentication

Code below:

import tweepy
import os

consumera = os.environ.get('TWICK')
consumerb = os.environ.get('TWICS')
accessa = os.environ.get('TWIAT')
accessb = os.environ.get('TWIATS')

auth = tweepy.OAuthHandler(consumera, consumerb)
auth.set_access_token(accessa, accessb)

api = tweepy.API(auth)

status = api.update_status(status="Test tweet.")

I've tried using other authentication methods, such as:

consumera = os.environ.get('TWICK')
consumerb = os.environ.get('TWICS')
accessa = os.environ.get('TWIAT')
accessb = os.environ.get('TWIATS')

client = tweepy.Client(consumer_key=consumera,
                       consumer_secret=consumerb,
                       access_token=accessa,
                       access_token_secret=accessb
                       )

Any fix?

Additional info: I was planning to run it through GitHub actions but without exposing the keys in the source code - and I put all the keys as secrets, so it requires environmental access. Tested on Ubuntu (both local and under GitHub Actions), but no luck.