SHOW_GRAVATAR_IMAGE ignored

After upgrading form 3.1 to 3.5 the environment variable 
SHOW_GRAVATAR_IMAGE is not being processed anymore, or rather: it still 
loads data from an unsolicited third party and tells them the mail 
address of the pgadmin user.

docker-compose.yml:

…
    environment:
        - SHOW_GRAVATAR_IMAGE=False
…

docker exec -ti pgadmin sh

/pgadmin4 # echo $SHOW_GRAVATAR_IMAGE
False
/pgadmin4 # grep -i gravatar ./config.py
# Allow users to display Gravatar image for their username in Server 
mode
SHOW_GRAVATAR_IMAGE = True

What can I do about that?