fix crash when RG fields set to null

In general, we convert None values to type-based nulls in packed fields just
as we do for normal fields.

beets/mediafile.py

@@ -306,18 +306,23 @@ class Packed(object):
     """Makes a packed list of values subscriptable. To access the packed
     output after making changes, use packed_thing.items.
     """
-    def __init__(self, items, packstyle, none_val=0, out_type=int):
+    def __init__(self, items, packstyle, out_type=int):
         """Create a Packed object for subscripting the packed values in
         items. The items are packed using packstyle, which is a value
-        from the packing enum. none_val is returned from a request when
-        no suitable value is found in the items. Values are converted to
-        out_type before they are returned.
+        from the packing enum. Values are converted to out_type before
+        they are returned.
         """
         self.items = items
         self.packstyle = packstyle
-        self.none_val = none_val
         self.out_type = out_type
 
+        if out_type is int:
+            self.none_val = 0
+        elif out_type is float:
+            self.none_val = 0.0
+        else:
+            self.none_val = None
+
     def __getitem__(self, index):
         if not isinstance(index, int):
             raise TypeError('index must be an integer')
@@ -352,6 +357,10 @@ class Packed(object):
             return _safe_cast(self.out_type, out)
 
     def __setitem__(self, index, value):
+        # Interpret null values.
+        if value is None:
+            value = self.none_val
+
         if self.packstyle in (packing.SLASHED, packing.TUPLE, packing.SC):
             # SLASHED, TUPLE and SC are always two-item packings
             length = 2

docs/changelog.rst

@@ -12,6 +12,7 @@ Changelog
   crashing.
 * 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.
 * Fix a crash when iTunes Sound Check tags contained invalid data.
 * Fix an error when the configuration file (``config.yaml``) is completely
   empty.

test/test_mediafile.py

@@ -189,6 +189,7 @@ class ZeroLengthMediaFile(beets.mediafile.MediaFile):
         return 0.0
 class MissingAudioDataTest(unittest.TestCase):
     def setUp(self):
+        super(MissingAudioDataTest, self).setUp()
         path = os.path.join(_common.RSRC, 'full.mp3')
         self.mf = ZeroLengthMediaFile(path)
 
@@ -198,6 +199,7 @@ class MissingAudioDataTest(unittest.TestCase):
 
 class TypeTest(unittest.TestCase):
     def setUp(self):
+        super(TypeTest, self).setUp()
         path = os.path.join(_common.RSRC, 'full.mp3')
         self.mf = beets.mediafile.MediaFile(path)
 
@@ -205,6 +207,22 @@ class TypeTest(unittest.TestCase):
         self.mf.year = '2009'
         self.assertEqual(self.mf.year, 2009)
 
+    def test_set_replaygain_gain_to_none(self):
+        self.mf.rg_track_gain = None
+        self.assertEqual(self.mf.rg_track_gain, 0.0)
+
+    def test_set_replaygain_peak_to_none(self):
+        self.mf.rg_track_peak = None
+        self.assertEqual(self.mf.rg_track_peak, 0.0)
+
+    def test_set_year_to_none(self):
+        self.mf.year = None
+        self.assertEqual(self.mf.year, 0)
+
+    def test_set_track_to_none(self):
+        self.mf.track = None
+        self.assertEqual(self.mf.track, 0)
+
 class SoundCheckTest(unittest.TestCase):
     def test_round_trip(self):
         data = beets.mediafile._sc_encode(1.0, 1.0)