artwork: fix artwork path computation with CUSTOM + empty filename

sonata/artwork.py

@@ -102,7 +102,12 @@ def path(self, artist, album, song_dir, specific_kind=None):
         if specific_kind is None:
             specific_kind = self.config.art_location
 
-        return next(iter(locations_map[specific_kind]))
+        try:
+            result = next(iter(locations_map[specific_kind]))
+        except StopIteration: # We tried an empty location :(
+            result = None
+        return result
+
 
     def path_from_song(self, song, specific_kind=None):
         """Same as `path()` but using a Song object."""

sonata/tests/test_artwork.py

@@ -88,6 +88,14 @@ def test_find_path_from_data_as_custom_dot_jpg(self):
         res = self._call_artwork_path_from_data()
         self.assertEqual('/foo/To/Ta/bar.png', res)
 
+    def test_find_path_from_data_as_custom_without_filename(self):
+        self.config.art_location_custom_filename = ""
+        self.config.art_location = consts.ART_LOCATION_CUSTOM
+
+        res = self._call_artwork_path_from_data()
+        # We tried CUSTOM without a valid custom filename :/
+        self.assertEqual(None, res)
+
     def test_find_path_from_data_force_location_type(self):
         self.config.art_location = "foo bar" # Should not be used