fromfilename: fix #460: crash w/ no capture groups

beetsplug/fromfilename.py

@@ -73,7 +73,10 @@ def all_matches(names, pattern):
     matches = {}
     for item, name in names.items():
         m = re.match(pattern, name, re.IGNORECASE)
-        if m:
+        if m and m.groupdict():
+            # Only yield a match when the regex applies *and* has
+            # capture groups. Otherwise, no information can be extracted
+            # from the filename.
             matches[item] = m.groupdict()
         else:
             return None

docs/changelog.rst

@@ -49,6 +49,8 @@ Other little fixes:
 * The importer now uses the album artist field when guessing existing
   metadata for albums (rather than just the track artist field). Thanks to
   geigerzaehler.
+* :doc:`/plugins/fromfilename`: Fix a crash when a filename contained only a
+  track number (e.g., ``02.mp3``).
 
 
 1.3.2 (December 22, 2013)