diff --git a/preparator.py b/preparator.py
index a705a5c..8e18d8c 100644
--- a/preparator.py
+++ b/preparator.py
@@ -171,7 +171,7 @@ def get_sets(mentions):
     for mention in mentions:
         if not mention.attrib['mention_head'] in POSSIBLE_HEADS:
             all_mentions.append(mention.attrib['span'])
-        
+
         set_id = mention.attrib['mention_group']
         if set_id == 'empty' or set_id == '' or mention.attrib['mention_head'] in POSSIBLE_HEADS:
             pass