From 32e84f3725ff015080131d6aaa40c7a832e115b2 Mon Sep 17 00:00:00 2001
From: Juerd Waalboer <juerd@tnx.nl>
Date: Wed, 6 Nov 2019 17:43:31 +0100
Subject: [PATCH] Fix that 'changed' would return true just because the
 attribute existed :)

Another option would have been to implement 'delete_attribute'.
---
 lib/RevBank/Cart/Entry.pm | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/RevBank/Cart/Entry.pm b/lib/RevBank/Cart/Entry.pm
index ef8950c..5ed1fe7 100644
--- a/lib/RevBank/Cart/Entry.pm
+++ b/lib/RevBank/Cart/Entry.pm
@@ -41,7 +41,10 @@ sub add_contra {
 sub has_attribute {
     my ($self, $key) = @_;
 
-    return exists $self->{attributes}->{$key};
+    return (
+        exists      $self->{attributes}->{$key}
+        and defined $self->{attributes}->{$key}
+    );
 }
 
 sub attribute {