diff --git a/taiga/projects/history/models.py b/taiga/projects/history/models.py
index d24806f6..5d1dd08b 100644
--- a/taiga/projects/history/models.py
+++ b/taiga/projects/history/models.py
@@ -181,9 +181,9 @@ class HistoryEntry(models.Model):
                 value_in = None
                 value_out = None
                 if diff_in:
-                    value_in = ", ".join([resolve_value("users", x) for x in diff_in])
+                    value_in = ", ".join([resolve_value("users", x) for x in diff_in if x])
                 if diff_out:
-                    value_out = ", ".join([resolve_value("users", x) for x in diff_out])
+                    value_out = ", ".join([resolve_value("users", x) for x in diff_out if x])
                 value = [value_in, value_out]
             elif key == "points":
                 points = {}