From ff92bb1a78da8a7168d25a3a8a73b5b6407e3153 Mon Sep 17 00:00:00 2001
From: Sasha Mitchell <sash.t.mitchell@gmail.com>
Date: Sat, 3 Oct 2026 02:04:24 +0700
Subject: [PATCH] fix: Scan(nil) clears a previous ULID

A NULL scan returned success and left the previous value in place, so a reused destination still looked like the old id. NULL now stores the zero ULID.
---
 ulid.go      |  1 +
 ulid_test.go | 10 ++++++++++
 2 files changed, 11 insertions(+)

diff --git a/ulid.go b/ulid.go
index e07e1a6..d7ebb5d 100644
--- a/ulid.go
+++ b/ulid.go
@@ -501,6 +501,7 @@ func (id ULID) Compare(other ULID) int {
 func (id *ULID) Scan(src interface{}) error {
 	switch x := src.(type) {
 	case nil:
+		*id = Zero
 		return nil
 	case string:
 		return id.UnmarshalText([]byte(x))
diff --git a/ulid_test.go b/ulid_test.go
index afa194b..a268eb0 100644
--- a/ulid_test.go
+++ b/ulid_test.go
@@ -555,6 +555,16 @@ func TestOverflowHandling(t *testing.T) {
 	}
 }
 
+func TestScanNilClears(t *testing.T) {
+	id := ulid.MustParse("01ARYZ6S410000000000000000")
+	if err := id.Scan(nil); err != nil {
+		t.Fatal(err)
+	}
+	if !id.IsZero() {
+		t.Fatalf("got %s, want zero", id)
+	}
+}
+
 func TestScan(t *testing.T) {
 	id := ulid.MustNew(123, crand.Reader)