diff --git a/src/calibre/customize/profiles.py b/src/calibre/customize/profiles.py
index 54c4259678..017bf86efb 100644
--- a/src/calibre/customize/profiles.py
+++ b/src/calibre/customize/profiles.py
@@ -617,6 +617,8 @@ class KindleDXOutput(OutputProfile):
     #comic_screen_size         = (741, 1022)
     supports_mobi_indexing = True
     periodical_date_in_title = False
+	missing_char = u'x\u2009'
+	empty_ratings_char = u'\u2606'
     ratings_char = u'\u2605'
     read_char = u'\u2713'
     mobi_ems_per_blockquote = 2.0
diff --git a/src/calibre/library/catalog.py b/src/calibre/library/catalog.py
index 0fb3f7138d..7d1dd47b08 100644
--- a/src/calibre/library/catalog.py
+++ b/src/calibre/library/catalog.py
@@ -1507,7 +1507,7 @@ class EPUB_MOBI(CatalogPlugin):
                     notes = self.__db.get_field(record['id'],
                                         self.opts.header_note_source_field,
                                         index_is_id=True)
-                    if field_md['datatype'] == 'datetime':
+                    if notes and field_md['datatype'] == 'datetime':
                         # Reformat date fields to match UI presentation: dd MMM YYYY
                         notes = format_date(notes,'dd MMM yyyy')