diff --git a/internal/infrastructure/database/repository.go b/internal/infrastructure/database/repository.go
index d5d0e89..af90762 100644
--- a/internal/infrastructure/database/repository.go
+++ b/internal/infrastructure/database/repository.go
@@ -18,6 +18,37 @@ func NewSignatureRepository(db *sql.DB) *SignatureRepository {
 	return &SignatureRepository{db: db}
 }
 
+// scanSignature scans a row into a Signature, handling NULL values properly
+func scanSignature(scanner interface {
+	Scan(dest ...interface{}) error
+}, signature *models.Signature) error {
+	var userName sql.NullString
+	err := scanner.Scan(
+		&signature.ID,
+		&signature.DocID,
+		&signature.UserSub,
+		&signature.UserEmail,
+		&userName,
+		&signature.SignedAtUTC,
+		&signature.PayloadHash,
+		&signature.Signature,
+		&signature.Nonce,
+		&signature.CreatedAt,
+		&signature.Referer,
+		&signature.PrevHash,
+	)
+	if err != nil {
+		return err
+	}
+	// Convert sql.NullString to string (empty string if NULL)
+	if userName.Valid {
+		signature.UserName = userName.String
+	} else {
+		signature.UserName = ""
+	}
+	return nil
+}
+
 func (r *SignatureRepository) Create(ctx context.Context, signature *models.Signature) error {
 	query := `
 		INSERT INTO signatures (doc_id, user_sub, user_email, user_name, signed_at, payload_hash, signature, nonce, referer, prev_hash)
@@ -25,12 +56,18 @@ func (r *SignatureRepository) Create(ctx context.Context, signature *models.Sign
 		RETURNING id, created_at
 	`
 
+	// Convert empty string to NULL for user_name
+	var userName sql.NullString
+	if signature.UserName != "" {
+		userName = sql.NullString{String: signature.UserName, Valid: true}
+	}
+
 	err := r.db.QueryRowContext(
 		ctx, query,
 		signature.DocID,
 		signature.UserSub,
 		signature.UserEmail,
-		signature.UserName,
+		userName,
 		signature.SignedAtUTC,
 		signature.PayloadHash,
 		signature.Signature,
@@ -49,25 +86,12 @@ func (r *SignatureRepository) Create(ctx context.Context, signature *models.Sign
 func (r *SignatureRepository) GetByDocAndUser(ctx context.Context, docID, userSub string) (*models.Signature, error) {
 	query := `
 		SELECT id, doc_id, user_sub, user_email, user_name, signed_at, payload_hash, signature, nonce, created_at, referer, prev_hash
-		FROM signatures 
+		FROM signatures
 		WHERE doc_id = $1 AND user_sub = $2
 	`
 
 	signature := &models.Signature{}
-	err := r.db.QueryRowContext(ctx, query, docID, userSub).Scan(
-		&signature.ID,
-		&signature.DocID,
-		&signature.UserSub,
-		&signature.UserEmail,
-		&signature.UserName,
-		&signature.SignedAtUTC,
-		&signature.PayloadHash,
-		&signature.Signature,
-		&signature.Nonce,
-		&signature.CreatedAt,
-		&signature.Referer,
-		&signature.PrevHash,
-	)
+	err := scanSignature(r.db.QueryRowContext(ctx, query, docID, userSub), signature)
 
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
@@ -98,21 +122,7 @@ func (r *SignatureRepository) GetByDoc(ctx context.Context, docID string) ([]*mo
 	var signatures []*models.Signature
 	for rows.Next() {
 		signature := &models.Signature{}
-		err := rows.Scan(
-			&signature.ID,
-			&signature.DocID,
-			&signature.UserSub,
-			&signature.UserEmail,
-			&signature.UserName,
-			&signature.SignedAtUTC,
-			&signature.PayloadHash,
-			&signature.Signature,
-			&signature.Nonce,
-			&signature.CreatedAt,
-			&signature.Referer,
-			&signature.PrevHash,
-		)
-		if err != nil {
+		if err := scanSignature(rows, signature); err != nil {
 			continue
 		}
 		signatures = append(signatures, signature)
@@ -140,21 +150,7 @@ func (r *SignatureRepository) GetByUser(ctx context.Context, userSub string) ([]
 	var signatures []*models.Signature
 	for rows.Next() {
 		signature := &models.Signature{}
-		err := rows.Scan(
-			&signature.ID,
-			&signature.DocID,
-			&signature.UserSub,
-			&signature.UserEmail,
-			&signature.UserName,
-			&signature.SignedAtUTC,
-			&signature.PayloadHash,
-			&signature.Signature,
-			&signature.Nonce,
-			&signature.CreatedAt,
-			&signature.Referer,
-			&signature.PrevHash,
-		)
-		if err != nil {
+		if err := scanSignature(rows, signature); err != nil {
 			continue
 		}
 		signatures = append(signatures, signature)
@@ -195,26 +191,13 @@ func (r *SignatureRepository) CheckUserSignatureStatus(ctx context.Context, docI
 func (r *SignatureRepository) GetLastSignature(ctx context.Context) (*models.Signature, error) {
 	query := `
 		SELECT id, doc_id, user_sub, user_email, user_name, signed_at, payload_hash, signature, nonce, created_at, referer, prev_hash
-		FROM signatures 
-		ORDER BY id DESC 
+		FROM signatures
+		ORDER BY id DESC
 		LIMIT 1
 	`
 
 	signature := &models.Signature{}
-	err := r.db.QueryRowContext(ctx, query).Scan(
-		&signature.ID,
-		&signature.DocID,
-		&signature.UserSub,
-		&signature.UserEmail,
-		&signature.UserName,
-		&signature.SignedAtUTC,
-		&signature.PayloadHash,
-		&signature.Signature,
-		&signature.Nonce,
-		&signature.CreatedAt,
-		&signature.Referer,
-		&signature.PrevHash,
-	)
+	err := scanSignature(r.db.QueryRowContext(ctx, query), signature)
 
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
@@ -243,21 +226,7 @@ func (r *SignatureRepository) GetAllSignaturesOrdered(ctx context.Context) ([]*m
 	var signatures []*models.Signature
 	for rows.Next() {
 		signature := &models.Signature{}
-		err := rows.Scan(
-			&signature.ID,
-			&signature.DocID,
-			&signature.UserSub,
-			&signature.UserEmail,
-			&signature.UserName,
-			&signature.SignedAtUTC,
-			&signature.PayloadHash,
-			&signature.Signature,
-			&signature.Nonce,
-			&signature.CreatedAt,
-			&signature.Referer,
-			&signature.PrevHash,
-		)
-		if err != nil {
+		if err := scanSignature(rows, signature); err != nil {
 			continue
 		}
 		signatures = append(signatures, signature)
diff --git a/internal/infrastructure/database/repository_constraints_test.go b/internal/infrastructure/database/repository_constraints_test.go
index 2ec12d9..198a0ec 100644
--- a/internal/infrastructure/database/repository_constraints_test.go
+++ b/internal/infrastructure/database/repository_constraints_test.go
@@ -62,7 +62,7 @@ func TestRepository_DatabaseConstraints_Integration(t *testing.T) {
 			{
 				name: "valid signature with nulls",
 				modifyFn: func(s *models.Signature) {
-					s.UserName = nil
+					s.UserName = ""
 					s.Referer = nil
 					s.PrevHash = nil
 				},
@@ -403,7 +403,7 @@ func TestRepository_EdgeCases_Integration(t *testing.T) {
 		// Test with empty strings for nullable fields
 		sig := factory.CreateValidSignature()
 		emptyString := ""
-		sig.UserName = &emptyString
+		sig.UserName = emptyString
 		sig.Referer = &emptyString
 		sig.PrevHash = &emptyString
 
@@ -418,7 +418,7 @@ func TestRepository_EdgeCases_Integration(t *testing.T) {
 		}
 
 		// Verify empty strings are preserved (not converted to NULL)
-		if result.UserName == nil || *result.UserName != "" {
+		if result.UserName != "" {
 			t.Error("Empty string UserName not preserved")
 		}
 		if result.Referer == nil || *result.Referer != "" {