From 203a75ee4a2fd508edd6c2df97a956e676edcb07 Mon Sep 17 00:00:00 2001
From: sonnemusk <sonnemusk@gmail.com>
Date: Wed, 22 Jul 2026 15:31:16 +0800
Subject: [PATCH] fix: treat empty string/bytes as NULL in NullUUID.Scan

UUID.Scan("") succeeds with a Nil UUID, so NullUUID.Scan previously set
Valid=true for empty DB values. Treat empty string and empty []byte as
SQL NULL (Valid=false), matching NullUUID.Scan(nil). Fixes #109.
---
 null.go      | 15 +++++++++++++++
 null_test.go | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/null.go b/null.go
index d7fcbf2..e04f408 100644
--- a/null.go
+++ b/null.go
@@ -38,6 +38,21 @@ func (nu *NullUUID) Scan(value interface{}) error {
 		return nil
 	}
 
+	// Treat empty database values as NULL. UUID.Scan("") leaves a Nil UUID
+	// and returns nil, which would otherwise mark Valid=true (issue #109).
+	switch v := value.(type) {
+	case string:
+		if v == "" {
+			nu.UUID, nu.Valid = Nil, false
+			return nil
+		}
+	case []byte:
+		if len(v) == 0 {
+			nu.UUID, nu.Valid = Nil, false
+			return nil
+		}
+	}
+
 	err := nu.UUID.Scan(value)
 	if err != nil {
 		nu.Valid = false
diff --git a/null_test.go b/null_test.go
index fe0fe8d..a8317bb 100644
--- a/null_test.go
+++ b/null_test.go
@@ -212,3 +212,37 @@ func TestNullUUIDUnmarshalJSON(t *testing.T) {
 		t.Errorf("expected nil when unmarshalling null, got %s", err)
 	}
 }
+
+func TestNullUUIDScanEmpty(t *testing.T) {
+	var nu NullUUID
+	// Start from a valid value to ensure empty clears Valid.
+	if err := nu.Scan("12345678-abcd-1234-abcd-0123456789ab"); err != nil {
+		t.Fatalf("setup scan: %v", err)
+	}
+	if !nu.Valid {
+		t.Fatal("expected Valid after setup")
+	}
+
+	if err := nu.Scan(""); err != nil {
+		t.Fatalf("empty string scan: %v", err)
+	}
+	if nu.Valid {
+		t.Error("expected Valid=false after scanning empty string")
+	}
+	if nu.UUID != Nil {
+		t.Errorf("expected Nil UUID after empty string, got %v", nu.UUID)
+	}
+
+	if err := nu.Scan("12345678-abcd-1234-abcd-0123456789ab"); err != nil {
+		t.Fatalf("re-setup scan: %v", err)
+	}
+	if err := nu.Scan([]byte{}); err != nil {
+		t.Fatalf("empty []byte scan: %v", err)
+	}
+	if nu.Valid {
+		t.Error("expected Valid=false after scanning empty []byte")
+	}
+	if nu.UUID != Nil {
+		t.Errorf("expected Nil UUID after empty []byte, got %v", nu.UUID)
+	}
+}