Assume that an empty list is an empty field

Author: snejus

beets/autotag/__init__.py

@@ -127,7 +127,7 @@ def _apply_metadata(
 
         # Don't overwrite fields with empty values unless the
         # field is explicitly allowed to be overwritten.
-        if value is None and field not in nullable_fields:
+        if (value is None or value == []) and field not in nullable_fields:
             continue
 
         db_obj[field] = value

docs/changelog.rst

@@ -36,9 +36,12 @@ New features
   3. Comma followed by a space
   4. Slash wrapped by spaces
 
-..
-    Bug fixes
-    ~~~~~~~~~
+Bug fixes
+~~~~~~~~~
+
+- Fix an issue with autotagging where an empty list was previously not
+  considered as an 'empty' value, which caused beets to overwrite existing
+  metadata with empty values instead of leaving them unchanged. :bug:`6403`
 
 For plugin developers
 ~~~~~~~~~~~~~~~~~~~~~

test/test_autotag.py

@@ -229,7 +229,6 @@ def setUp(self):
             },
         ]
 
-    @pytest.mark.xfail(reason="Album genres are not applied to tracks")
     def test_autotag_items(self):
         self._apply()