diff --git a/pyaccuwage/pdfextract.py b/pyaccuwage/pdfextract.py
index ef9a023..cb60870 100644
--- a/pyaccuwage/pdfextract.py
+++ b/pyaccuwage/pdfextract.py
@@ -201,7 +201,10 @@ class ColumnCollector(object):
         pass
 
     def __repr__(self):
-        return "<%s: %s>" % (self.__class__.__name__, map(lambda x:x if len(x) < 25 else x[:25] + '..', self.data.values()))
+        return "<%s: %s>" % (
+				self.__class__.__name__,
+				map(lambda x:x if len(x) < 25 else x[:25] + '..',
+				self.data.values() if self.data else '' ))
 
     def add(self, data):
         #if self.empty_rows > 2: