Prevent null logging options in `docker-compose config` output

Signed-off-by: Joffrey F <joffrey@docker.com>

compose/config/config.py

@@ -1044,8 +1044,8 @@ def merge_logging(base, override):
     md.merge_scalar('driver')
     if md.get('driver') == base.get('driver') or base.get('driver') is None:
         md.merge_mapping('options', lambda m: m or {})
-    else:
-        md['options'] = override.get('options')
+    elif override.get('options'):
+        md['options'] = override.get('options', {})
     return dict(md)
 
 

tests/unit/config/config_test.py

@@ -1864,7 +1864,6 @@ class ConfigTest(unittest.TestCase):
             'image': 'alpine:edge',
             'logging': {
                 'driver': 'syslog',
-                'options': None
             }
         }