fix(user): don't match a commit with an empty author email to a user (#39777)

Fixes https://github.com/go-gitea/gitea/issues/39776

models/user/user.go

@@ -1231,6 +1231,9 @@ func GetUsersByEmails(ctx context.Context, emails []string) (*EmailUserMap, erro
 	noReplyAddressSuffix := "@" + strings.ToLower(setting.Service.NoReplyAddress)
 	for _, email := range emails {
 		emailLower := strings.ToLower(email)
+		if emailLower == "" {
+			continue // a commit without an author email names no user
+		}
 		needCheckEmails.Add(emailLower)
 		if localPart, ok := strings.CutSuffix(emailLower, noReplyAddressSuffix); ok {
 			name, id := parseLocalPartToNameID(localPart)

models/user/user_test.go

@@ -96,6 +96,12 @@ func TestUserEmails(t *testing.T) {
 			setting.Service.NoReplyAddress = "example.com"
 			testGetUserByEmail(t, "user1-2@example.COM", 1)
 		})
+
+		t.Run("EmptyEmail", func(t *testing.T) {
+			// A user whose email address is empty must not own commits that have no author email.
+			require.NoError(t, db.Insert(t.Context(), &user_model.EmailAddress{UID: 2, Email: "", LowerEmail: "", IsActivated: true}))
+			testGetUserByEmail(t, "", 0)
+		})
 	})
 	t.Run("GetUserByEmail", func(t *testing.T) {
 		testGetUserByEmail := func(t *testing.T, email string, uid int64) {