diff --git a/types.go b/types.go
index 5c1c55e..551b5c5 100644
--- a/types.go
+++ b/types.go
@@ -64,6 +64,9 @@ type User struct {
 // It is normally a user's username, but falls back to a first/last
 // name as available.
 func (u *User) String() string {
+	if u == nil {
+		return ""
+	}
 	if u.UserName != "" {
 		return u.UserName
 	}