diff --git a/libcovebods/utils.py b/libcovebods/utils.py
index 97be836..e638237 100644
--- a/libcovebods/utils.py
+++ b/libcovebods/utils.py
@@ -70,7 +70,8 @@ def sort_by_date(list_with_date, index):
     out = []
     for item in list_with_date:
         date = parse_date_field(item[index])
-        new_item = item.copy()
-        new_item[index] = date
-        out.append(new_item)
+        if date:
+            new_item = item.copy()
+            new_item[index] = date
+            out.append(new_item)
     return sorted(out, key=lambda x: x[index])