#19 if we didn't defined anenvironment variable, just leave ALLOWED_HOSTS as it is

project/settings/hosts.py

@@ -10,5 +10,5 @@ from .env import DEBUG
 
 if DEBUG:
     ALLOWED_HOSTS = ['*']
-else:
+elif 'DJANGO_ALLOWED_HOSTS' in os.environ:
     ALLOWED_HOSTS = [os.environ['DJANGO_ALLOWED_HOSTS']]