fix(ftintitle): remove singleton handling as out of scope

beetsplug/ftintitle.py

@@ -117,20 +117,14 @@ def find_feat_part(
     """Attempt to find featured artists in the item's artist fields and
     return the results. Returns None if no featured artist found.
     """
-    if not albumartist:
-        _, feat_part = split_on_feat(
-            artist, for_artist=True, custom_words=custom_words
-        )
-        return feat_part
-
     # If the album artist is featured, move the remaining artist to the title.
     artist_part, feat_part = split_on_feat(artist, custom_words=custom_words)
-    if feat_part == albumartist and artist_part:
+    if albumartist and feat_part == albumartist and artist_part:
         return artist_part
 
     # Handle a wider variety of extraction cases if the album artist is
     # contained within the track artist.
-    if albumartist in artist:
+    if albumartist and albumartist in artist:
         albumartist_split = artist.split(albumartist, 1)
 
         # If the last element of the split (the right-hand side of the

test/plugins/test_ftintitle.py

@@ -281,14 +281,6 @@ class TestFtInTitlePluginFunctional(PluginTestHelper):
                 "Song",
                 id="no-feature",
             ),
-            pytest.param(
-                {"auto": True},
-                "Alice & Bob",
-                "Song",
-                "Alice",
-                "Song feat. Bob",
-                id="generic-separator-singleton",
-            ),
             pytest.param(
                 {"auto": True},
                 "Alice feat. Bob",
@@ -434,7 +426,6 @@ class TestFtInTitlePluginFunctional(PluginTestHelper):
         ("Alice & Bob", "Bob", "Alice"),
         ("Alice ft. Bob", "Bob", "Alice"),
         ("Alice ft. Carol", "Bob", "Carol"),
-        ("Alice & Bob", "", "Bob"),
     ],
 )
 def test_find_feat_part(