format None values as the empty string

Fix due to @pscn. Includes test. Closes #108.

beets/library.py

@@ -218,6 +218,8 @@ def format_for_path(value, key=None, pathmod=None):
     elif key == 'samplerate':
         # Sample rate formatted as kHz.
         value = u'%ikHz' % ((value or 0) // 1000)
+    elif value is None:
+        value = u''
     else:
         value = unicode(value)
 

docs/changelog.rst

@@ -24,6 +24,8 @@ Other stuff:
 * When the importer encounters an error (insufficient permissions, for
   example) when walking a directory tree, it now logs an error instead of
   crashing.
+* In path formats, null database values now expand to the empty string instead
+  of the string "None".
 * Add "System Volume Information" (an internal directory found on some
   Windows filesystems) to the default ignore list.
 * Fix a crash when ReplayGain values were set to null.

test/test_db.py

@@ -362,6 +362,10 @@ class DestinationTest(unittest.TestCase):
         val = beets.library.format_for_path(12345, 'samplerate', posixpath)
         self.assertEqual(val, u'12kHz')
 
+    def test_component_sanitize_none(self):
+        val = beets.library.format_for_path(None, 'foo', posixpath)
+        self.assertEqual(val, u'')
+
     def test_artist_falls_back_to_albumartist(self):
         self.i.artist = ''
         self.i.albumartist = 'something'