diff --git a/src/calibre/library/cli.py b/src/calibre/library/cli.py
index 75f72297a4..1ac82b2edb 100644
--- a/src/calibre/library/cli.py
+++ b/src/calibre/library/cli.py
@@ -126,7 +126,8 @@ def do_list(db, fields, sort_by, ascending, search_text, line_width, separator,
     fields = ['id'] + fields
     if output_format == 'text':
         for f in data:
-            f['formats'] = u'[%s]'%u','.join(f['formats'])
+            fmts = [x for x in f['formats'] if x is not None]
+            f['formats'] = u'[%s]'%u','.join(fmts)
         widths = list(map(lambda x : 0, fields))
         for record in data:
             for f in record.keys():
diff --git a/src/calibre/library/database2.py b/src/calibre/library/database2.py
index 194933bb3a..18765e3e3c 100644
--- a/src/calibre/library/database2.py
+++ b/src/calibre/library/database2.py
@@ -1525,6 +1525,8 @@ class LibraryDatabase2(LibraryDatabase):
             if formats:
                 for fmt in formats.split(','):
                     path = self.format_abspath(x['id'], fmt, index_is_id=True)
+                    if path is None:
+                        continue
                     if prefix != self.library_path:
                         path = os.path.relpath(path, self.library_path)
                         path = os.path.join(prefix, path)