diff --git a/build_db.py b/build_db.py
index c78e0da..82bdcea 100644
--- a/build_db.py
+++ b/build_db.py
@@ -12,13 +12,10 @@ with open('db.sql') as file:
 
 data = pyexcel_odsr.get_data('reference.ods')
 
-def nullifempty(cell):
-    return None if len(cell)==0 else cell
-
 # import song
 cur.executemany(
     'insert or ignore into song(id,name,name_jp) values(?, ?, ?)',
-    ((row[0],row[3],None if len(row)<5 else nullifempty(row[4])) for row in data['Song'][1:])
+    ((row[0],row[3],row[4]) for row in data['Song'][1:])
 )
 
 # import album
@@ -30,7 +27,7 @@ cur.executemany(
 # import artist
 cur.executemany(
     'insert into artist(id,name_rm,name) values(?, ?, ?)',
-    ((row[0],nullifempty(row[1]),row[2]) for row in data['Artist'][1:])
+    ((row[0],row[1],row[2]) for row in data['Artist'][1:])
 )
 
 # import credit
@@ -63,8 +60,6 @@ cur.executemany(
     creditparams(data['Song'])
 )
 
-# import song x album
-#    "insert into song_album(album_id,track,song_id) values (?, ?, (select id from song where name = ? and coalesce(name_jp,'') = coalesce(?,'')))"
 cur.executemany(
     "insert into song_album(song_id,album_id,track) values (?, ?, ?)",
     ((row[0],row[1],row[2]) for row in data['Song'][1:])